Crothian said:But with 4 new systems, the system has a better chance to really effect the game. Some times d20 gamews even of different genres can feel similiar because of the similiar mechanics. Different mechanics really help differenciate games. However, while it may be easy for you as the guy running it the players might bulk at this idea of always learning a new system.
Let me also suggest that sometimes it IS easier to learn 4 new systems than one extremely complex one. Personally, I found it easier to learn Storyteller than d20 (picked it up very quickly cause it was just dirt simple - was my first system, too) and simple systems like Feng Shui, and Unknown armies are much easier to learn than d20. Now, AD&D2e, that I don't know - and I would imagine it would be more complex than d20.
Personally, I'd go with the system that gives you the best play experiences - because chances are if it's not D&D3e, you're going to be the guy running it anyway.