I have a Series 7 & I love it (last time they made a titanium model with the matte natural look). Works great. I:'ve had a 2,3, 4 (I think), 5,6,7 and while they are all nice, the 7 is the one for me. I'd upgrade again if they came out with another matte titanium model (the Ultra might be, but I don't care for that style). I think the 7 will last me for a long time. It has the larger screen (smaller than 10, but slightly larger than 6, etc) and the ability to type out texts using the onscreen keyboard.
My battery is at 80% & I'll defiantly get it replaced once it dips below that. I'll upgrade eventually, but sooner if they come out with one that I like a lot. But if not, the 7 is really great.
As far as battery, if you've only had it a few days, I'd say reserve judgement until you've had it a bit longer. I found that I played around with mine a lot at first & that used up more battery life than how I use it in day to day life. Also, if you just updated the system software, that always messes with battery life (for me) for a day or two.