Well, IMO, buy a good one and save your money.
I bought a smaller portable one, and honestly, its a piece of crap. Sure it might work sometimes, but it will not start the big stuff, and its far from reliable.
I have a Prestone (I think?) big yellow pack I got from walmart probably 7 years ago. That thing has saved me so many times I cant even count. I have also used it just as many or more times to start other peoples cars, and customers cars at work. It starts anything, first time, and hardly ever needs a charge. Its started everything from a 550cc motorcycle to my 455 big block Electra in the dead of winter. Even ended up in my flooded out Escort underwater, pulled it out, let it dry out, and used it that same day without it needing a charge to start my Cruiser.
I think it cost me $70-80 way back when.
You get what you pay for.
