"Better" is in the eye of the beholder.
I prefer the Riva-510. It is exactly the same size as the eGo (and fully compatible with all eGo attys, cartos,
tanks, and accessories), but is higher voltage (3.7V vs. 3.2V) and mAh (750 vs. 650) and less expensive (e.g., you can get a
full kit from Liberty-Flights for $30). However, if you still have your eGo charger (which works just as well with the Riva), you can purchase only a
Riva battery for $12. Any other battery I can think of (whether other fat batts or
mods) would be appreciably
larger than the 750 mAh Riva or 650 mAh eGo.
That's the battery issue. Another way to get "better" is with the atomizer or cartomizer ... and I strongly prefer
cartomizers. IMO atomizers are only suited for use with
juice feeders ... unless you really don't mind dripping. [I dripped for most of two years (when cartomizers weren't that great), but got
sick of it (and cartomizers now
are great).] Some of the best 510 cartos are the
Boge 2.0,
Smok Tech Mega Dual Coil, and
Smok Tech 1.7 ohm Mega Single Coil ("Resurrector"). [Links are to
examples of low-priced suppliers.]
My
personal favorite cartomizer today is the
Elite 808 from CigEasy. It is a Kr8 compatible, but I often use it with an inexpensive 510-to-808/901 adapter (e.g., from
Good Prophets) on my eGo and Riva batteries. [NOTE: The adapter extends the length by about 1/4 inch and, since the cartomizer is slightly wider than the typical 510, the eGo/Riva cone doesn't fit over it.]