are you using carts with the 901? or dripping? Most 901 attys have nice flavor, warm vapor. The biggest complaint for most (including me) is the propensity for the attys to leak. I've been using them most recently on a mod w' a 501/901 adapter and using a drip shield. It's a nice, finished look for when I drip.
I never used the 901 "stick" type batteries. My first foray into 901s was on a KR808D-1 battery, since the threads are identical. The batts are a little bigger (think 280mAh vs 180mAh). If you wanted to stick with the cig-type batts a bit longer, I'd recommend these over the standard 901 batts.
Do you have any particular direction you wanted to explore first? Cartos?
tanks? Clearomizers? higher Voltage/Watts?
A common recommendation from many on the forum, including myself, is to pick up an eGo-type device+charger, which offers alot of flexibility AFA cartos/tanks/attys/etc. Couple that with a 501/901 adapter and you can still use your 901 attys on this batt, plus alot more.