Ana it really depends what sort of a dish you are making, and what texture and flavour you are after and the nature of garlic state: chopped, crushed, minced, pounded, etc.
If you want that pungent taste of garlic to be tasted, then you could add these crushed, chopped, sliced ones into your dish in the middle stage. If you do not want to taste too much of garlic, but just to go along, then minced ones are better and you may add a vee-bit at the earlier stage of the cooking. (I had to edit this passage as I had written it swapping the stages)
Garlic can be used for both oil based and water based dishes. Even for salads without oil! but with some flavours of lemon/lime and salt. We usually blend one raw garlic clove (as per the quantity) when making guacamole!!!
So are you sauteing vegetables? Or a gravy based dish? Should the dish go alone or with another set of course based dishes? =)
Update as per OP's edit:----------
I must say it is quite rare to see chefs wanting to preserve the best pungent flavours of garlic/onions... ;)
Cooking the garlic by, say, roasting or frying it affects it in
another way: its flavor changes as chemicals break down and reform
into novel aromatic compounds. It also becomes sweeter as large sugars
and carbohydrates break down into simpler sugars like fructose and
glucose, both of which taste quite sweet to us.
The key to really great garlic flavor? Use a combination of techniques as indicated in the above article. Personally I like to do couple of things. Marinating with crushed/chopped/sliced garlic would be in your favour. The longer main-ingredients wrapped with raw garlic before cooking, the better they absorb the flavour as well as aroma. This only works for fast/short cooking dishes. Because longer cooking kills the pungency and makes the dish sweeter.
It all comes down to the chemistry of ingredients and heat - not to mention the experience you may get along!