I see a lot of threads from new multi-box users asking how is XYZ class combination for multi-boxing and I wanted to throw something out there for consideration.

For 2-boxing, there are 45 different class combinations
3-boxing, 165 class combinations
4-boxing, 495 class combinations
5-boxing, 1287 class combinations.

That doesn't even take talent tree focus into account. If you do, then for 5 boxing,
169,911 possible class and talent tree combinations!

My suggestion, try whatever you are considering and post your experiences here. Read about others experiences. Experimenting is a large part of multi-boxing, in my opinion.

I can only think of maybe two rules of thumb
1. Focus on DPS specs/classes for leveling and quest grinding
2. A healer and rezzer in your group will make things much easier

Outside of that, go play, experiment and let us know how it goes

EDITED: to fix my math