Gens Ace 25c gave me better punch than Turnigy 40c in my first big rig. For my new Hummer build I'll be running 6s - 2 of these in parallel:
http://www.hobbypartz.com/98p-25c-4000-6s1p.html
for 200Amps constant/400Amps burst rating
I've never tried the nanotechs - but reviews are mixed.