It's hard to figure out what's right for you if you've never tried anything to see what you don't like about it.
I've gone to an eGo for long battery life, a must for me, and to have lots of options for cartos, atties etc. The many options is a mixed blessing; I've spent a lot of money trying things I don't like, but I think I'm happy with the Mega atties now. Cartos are not for me, I've decided.
I think an inexpensive 510 kit might be a good way to start as you still have a lot of options to add to it and if you decide to go with an eGo later, your atties, cartos, whatever will fit it too. If, however, you know you want a longer battery life and don't mind a larger size, you should consider the eGo.
Keep in mind, I'm not saying the eGo is the absolute best thing out there for everyone; it's what's right for me. That's why I'll recommend an inexpensive kit to start so you can find out what you don't like about it and can then make a more informed choice about what's right for YOU.