Tiger vs Leopard

     Tiger                                 Leopard 

Easiest

Anything Older - Panther

G3 - Tiger

G4/G5 - Leopard

Specs

400Mhz - 600Mhz Panther
 700Mhz - 1.0Ghz Tiger
 1.2Ghz  - Any.Ghz Leopard

Tiger Advantages:

1. Faster
2. Matches G3 and First Gen G4 Macs
3. Is compatible with a lot of Applications.

Leopard Advantages:

1.  Most Compatiable with EVERYTHING (nufffff said)
2. Matches G4 - G5 Macs
3. THINGS JUST WORK

It's all about preferance, I would try both, I would suggest Tiger for a normal user since it is somewhat faster, and Leopard for a Power user since it supports more applications. Simple as that.

NOTE that Tiger will always be faster, so if you can get the applications you need on Tiger, I would recommend using it over Leopard.

-Peace out girl scout