I've had a selection of Lithium cells over the years.
I had 30 x 200ah TS cells 7 years ago and they were good until i over discharged them. I got four years road use out of them, might have lasted 6 years before IR got too high IMO. I still use about 20 of them in my windpower setup. I would buy TS again.
I've had a set of 50 x 40ah hipower cells for around two years now and they are good. I had one unexplained cell failure within first year but replaced free. (Get a couple of spares) They are now available in a new variant with higher power but slightly bigger/heavier. I am using the older highpower cells at the limit for regen and pushing 50A into them on occasion which probably explains my cell failure. I would buy them again as well, they are available from david cowperthwaite in UK.
I also have a set of 48 Lifebatt 8ah cells. They can deliver the current very well but are expensive. I would buy the 15ah variant if I used them again, the 8ah are a little small for my application and struggle with high regen 50A! They are available from Ian the UK Lifebatt rep.
I also have on order 52 x 20ah A123 pouch cells but can't report on them until I get them and they have been installed etc. On paper they look the best being light and with very good power/current delivery. You can get them from cell_man who posts on this forum. http://www.endless-sphere.com/forums/vi ... 14&t=15093
They don't look particulary easy to terminate though so that may be interesting.
The nut and bolt prismatic or cylindrical cells are very easy to deal with and interconnect.
In conclusion most modern lithium cells will perform fine so the choice comes down to cost/size/specs
Don't forget to factor in a BMS of some sort.