yeah, me too... the TimeBomb is a classic, Oakley's first watch and if you're considering a watch, that should be the first. the TimeTank is new so it'll be around for a while, maybe some new colours will be introduced in the future as well.
as for weight, like Mike says the Titanium TimeBomb versions are very light (i'd say probably even lighter than the TimeTank), the Stainless Steel versions are a bit heavier but to my unscientific experience, still not as heavy as, say... a Judge or a GMT.
i used to think the original hidden clasp looks nice but now i'll agree with Iggy that the newer overlapping clasp looks better... i think it's the big icon that i like about it LOL.