General reply will be to go optipower. However I would much rather have 2 batteries than one etc.

Everyone has their little horror stories with each brand, I have not had sucsess with the zippy series, dead cells etc but some people have a gold track record with them. All my robots over the past 2 years have run the hobbyking nanotech series without any fail, a couple of people have had issues with them but so long as you spec your battery properly you shouldnt have any issues.

A decent charger will make your battery care much much easier too I will add.