It takes more extreme care when handling a non-protected lipo battery like the max amps packs for instance.
You drop it on the ground and kiss it goodbye.

Nimh is cheaper to run, and most esc's nowadays can handle 10+ cells.

Lipo is different as it's divided in 1 cell, 2 cell, 3 cell, 4 cell and up!

Nimh doesnt need a pricey charger to charge packs up, I've been using my superbrain 960 and it has proven itself very well for a 60 dollar price tag.
Being digital is always a bonus also.

The more expensive the batt the usually the better. If you pay 80 dollars for a nimh you might as well save you some trouble and go lipo.
People at my local track prefer the Tracpower lipo packs due to being alot safer to handle and stuff.