I got an AGM from Autozone (because I was in a pinch for time) for about $100. It was a decent brand for motorcycles. AGM (absorbed glass mat) is generally a better than a standard lead acid battery. Also good to use a battery tender if you don't ride all the time.
Hi, I have used a few different batteries for my smaller quads and motorcycles. I just got a Grizzly and I would not put in anything but a Yuasa battery. I find they last a lot longer and I rather not replace the battery every 1-2 years. More money but well worth it.
I have gotten longer life out of AntiGravity lightweight batteries in my motorcycles than I ever have out of the OEM ones or replacement YUASA ones. I asked about them here before for ATV use. http://www.grizzlycentral.com/forum...ne-using-lightweight-lithium-ion-battery.html
I don't know why it wouldn't be a good option for ATVs. Maybe if you're running a bunch of accessories like a winch, hand warmers, and lighting...I don't know. Shouldn't affect it unless you try to run those accessories with the machine off. These batteries are unbelievably light and you get better cold weather starting out of them too in my experience.
Currently my Griz has a walmart battery from the PO. I've owned it 3 years with no problems until last week when it clicked a bit before finally starting. Charged battery overnight and keeping it on trickle charge since. With deer season coming soon I've been battery shopping proactively. I believe an AGM battery is probably the way to go for me, but being a frugal guy I'd like to find the best bang for the buck.