Trade Paints Vs Retail Paints
There is a general rule of thumb that retail paints are inferior to trade paints. The reasons for this are that Trade paints have to be full bodied paints because tradesmen require a certain level of versatility from them.
 We work on contracts of many different types and the paints we use have to be adaptable to cope with different methods of application and for working in different climatic conditions. 
Paint, for example, might need to be thinned down for use in spray machines or thinned down to seal or stabilize surfaces prior to painting. Retail paints will not generally be up to the job where this type of versatility is concerned because they have usually been 
thinned down already during the manufacturing process. Trade paints generally (though not always) will only require two coats to give a truly professional finish, where as retail paints  seem a bit lacking in this department.
One bit of advise you really should listen too about buying paint, is to avoid the really cheap paints that sit on the shelves in D.I.Y stores - you could end up having to apply four or even five coats to get anywhere near a finish that looks remotely respectable.
 (That's not an exaggeration!)

Solvent (Oil) based paints
pros - As a professional decorator, i would always prefer to use Solvent based paints. Solvent based paints are more durable and allow me to achieve a more professional finish. The paint flows over the surface and can be worked and layed off to achieve an even coat over the surface. Because of longer drying times, you are able to re-visit (re-touch with your brush) areas you have painted for quite some time.
cons - they are more difficult to apply than water based paints (the paint will run if applied too thickly) and though European regulations have recently forced paint manufacturers to remove V.O.C's (Volatile Organic Compounds) from their paints, they can still be quite odorous. Solvent based paints usually require 
16 hours drying time before they can be re-coated. Any spills or splashes cannot be cleaned with water - turps or white spirit is required. Cleaning brushes out after use with Solvent based paints is more difficult than with water based paints. 

Water based paints
pros - Water based paints for woodwork are easy to apply - very little finesse is required. They are low odour paints and are very quick drying. Any spills can be cleaned with water and brushes can easily and quickly be washed out after use.
acrylic paint

cons - The finish these paints offer is inferior to that of solvent based paints and are not as hard -wearing.  Once the paint is applied, it needs to be left to completely dry before you revisit it
with a paint brush - the paint will 'ruck' up if you re- touch wet paint with a brush.

Paint for your woodwork
Once you have decided whether to use solvent based paints or water based paints for your woodwork, you then have to choose the type of finish you need. Listed here are the most common finishes you will find for your woodwork.

Pros - Gloss finishes are the most hard-wearing  finishes available for your home and are completely scrubbable. If your surfaces are prepared well and are nice and smooth,    Glossed woodwork can give a really classy finish to your decor. 
Undercoat and Gloss

Cons -  Gloss reflects light so will highlight any imperfections on the surface you are painting.  You wont be able to touch the surface up without it being noticeable  if it becomes damaged.

Pros- Eggshell is very similar to satin. It might, (depending on the brand of paint you choose) be slightly less shiny than Satin. As the word suggests, if you can imagine the slight lustre 
of an eggshell - that is the type of finish you should expect. Eggshell gives a nice finish to your woodwork, is wipeable and because of its low sheen, any imperfections on your surfaces wont be highlighted. 
Cons - Eggshell is not as hard-wearing as gloss, and though it is wipeable, any scrubbing will be likely to damage the paintwork.  Again, as with gloss finishes, it can be difficult to touch up due to the slight sheen of the paint. 

satin finish
Pros - A  Satin finish is not as shiny as a gloss finish.  Satin offers a more 'velvety' appearance than gloss. Whereas glossed surfaces show up 
imperfections, a satin finish wont seem so critical. I personally feel that satin(and eggshell) offer a more cosy/warm feel to a room than a gloss finish that can sometimes feel a little clinical. 
Cons -  Not as hard-wearing as a gloss finish. The finish is wipeable, but wont be quite as scrubbable as a gloss finish. Can be difficult to touch up.

Walls and Ceilings
Emulsion paint is usually considered to be the best choice for painting walls and ceilings. It is a water based paint that comes in various guises.
 If you go to your local D.I.Y store or read literature from any paint manufacturer, you will find a whole range of different types of emulsion paints. There are paints specifically designed for new plaster work, there are paints designed specifically for kitchens and bathrooms, One-coat emulsions, flat Matt, durable Matt, high opacity Matt - the list these days seems endless, and different paint manufacturers give their own brand names to their own 'gimmicky' products.
There are that many different products on the shelves these days, i am in no position to offer any serious opinion about most of the brands,   
their ranges and their claims. What i can do is generalize paints by their finishes and offer some advise regarding their pros and cons.

Matt finishes
pros - Matt finishes absorb light and are perfect for concealing imperfections on walls. Matt finishes can seem warm and cosy making them perfect for bedrooms and living rooms (see picture below). The good thing about using Matt emulsion is that your walls can usually be touched up if they become marked. Matt emulsion doesn't 'flash' when wet paint is applied over a previously painted dry coat.  Matt emulsion is perfect for coating ceilings; there is no need for the surface to be washable and it hides the imperfections that tend to be very visible on ceilings. 

nursery decor

cons - Though Matt finishes are wipeable, any scrubbing will probably remove the paint from the wall.  So  if you choose a Matt finish in a high traffic area of your home, make sure you have enough paint left over to touch up the walls from time to time. 
In rooms that are subjected to high levels of condensation,  i would advise against using Matt emulsion and instead opt for a Satin or Silk finish.

Silk Finishes 
Pros - Silk gives a shiny finish that can look classy in the right place. Walls painted with silk will be more hard wearing than Matt finishes. Whilst a Matt finish is wipeable,  a Silk finish is scrubbable. It is the perfect paint to use in areas of high traffic or areas subject to high levels of condensation.
Cons - Can be problematic to apply for  
a D.I.Yer as it is essential to keep a 'wet edge' going to achieve an even coat.  If you allow your cutting in to dry before you manage to get your roller work done, then you will see a picture frame effect on your walls. It doesn't matter how many coats of paint you apply to the surface, if you don't keep that wet edge going during the application process, the 'picture frame' effect will remain.  Unlike Matt finishes, if a wall painted with Silk Emulsion is damaged, you wont be able to touch the paintwork up without seeing it 'flash' against the previously painted areas. You will probably have to re-coat an entire wall to avoid the 'flashing' problem.  The sheen of Silk emulsion reflects light and will highlight any imperfections on your walls/ceilings. Preparation work may have to be quite extensive to achieve a professional finish.

Satin Finishes 
pros - Satin emulsions offer a subtle sheen that can make a room look elegant and inviting. Satin is a little bit more hard wearing than Matt and though not Scrubbable, can be more vigorously  
Cons - The sheen reflects light so it is essential to carry out good surface preparation to make sure the walls are smooth. If the walls become damaged or marked, it can be difficult to touch up the paintwork without flashing occurring (It will depend on how light hits the surface and from what position the surface is viewed from).