re
rjtjrt's comment I think you'll find modern NiMH cells have significantly lower self-discharge than earlier units.
Lithium will tend to be lighter/smaller for same capacity however. The downside it that they may be harder to come by in later years if they're a special for that specific radio. Many NiMH batteries are made up of relatively standard cells so you can often break them open and replace them when the pack ages. If you could get a unit that used just standard 'AA' cells I'd definately go for that - it's great if your radio/GPS/camera can all share the same batteries, that way it's easy to carry spares and to swap around if the need arises.
Vertex (Yaesu) and Icom are both good manufacturers of long standing, in general either should give you a good run so I'd be inclined to make the choice on features/cost/personal preference (shape or colour I guess if you're female
........
). Definately a transceiver tho'!
FP.