I personally like the 3.7V boxmods from boxmods.net. They use a 14500, and actually work at 3.7V, unlike the ego which is about 3.1V. They are inexpensive (~$25), fit easily in the hand and pocket, and they have a master on-off switch for pocket carrying.
Box Mod
14500 batts are ~4 each, or less, and they will always be available, since they are used for all manner of electronic devices.'
Of course this does not negate the
popularity of the ego, and it is a good device. But I find attys clog less and last longer with a little added voltage.