1. Bethesda
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2. Raven
3. Splash Damage
4. Ensemble
5. Ubisoft

1. Nintendo EAD (whichever group makes the Zelda games)
2. Sega
3. Bioware
4. Intelligent Systems
5. Retro Studios

1. Nintendo - For their general excellence and proficiency and the 'fun' factor in their games and amazing innovation.

2. Davilex Games - For the two decent Knight Rider games they developed.

3. RockStar North - For the Grand Theft Auto series, one of the greatest (I'm ignoring the utter trash that was GTAIV).

4. Rare - For GoldenEye & Perfect Dark, two of the best shooting games to this day.

5. Intelligent Systems - For Advance Wars which are in my humble opinion the finest strategy games around.

After a little consideration my own top 5 are:

1. Nintendo (If we can count all their development studios as one then this isn't a very hard choice for me)
2. Rare (pre-microsoft)
3. Capcom
4. Konami
5. Bullfrog

1.Atlus
2.Konami
3.Naughty Dog
4.Sega
5.Capcom