Whatever you can afford. I got one that lasted me 5 years however during the move from South Carolina to Texas something happened to it amd it died I'll be looking for a new one later.
Right now i have an auto battery i got when I junked my van and am using a trickle charger on it to run my radio and scanner. [IF I need to i can unhook the charger and run it out to the car and jump start it with that].
I know this is a slightly old topic, but just FYI, I bought a jump-pack that had an LED spotlight built in along with an air compressor and it also claimed to be a 1000ca battery. I paid about $40 at a garage sale back in early 2006 (and it was still NIB.) It was pretty heavy. It would even help jump my 6.2 Chevy diesel over! It lasted me almost 5 years before it threw in the towel. If I can find out what the brand was, I will post it here! Best damn jumpbox I had ever toyed with =)