Eneloops aren't "beefy". Their mAh ratings are mediocre -- 2000 mAh when batteries claiming 3200 mAh are available. (Note that the really high mAh rated batteries tend to suck in other ways, even if they do achieve their rated capacity, which is iffy.)

However, their low discharge rates are totally worth it. Charge it today, use it six months from now -- it's ready to go. Low internal resistances as well.

Do you mean hefty as in heavy? Their size is limited by the AA specifications, and I haven't noticed them to be significantly heavier than other rechargeables.