I've started converting to AGM - they seem to have a much better performance - My Jeep actually came OE with an AGM and it's now over 3 years and still cranks like the day I bought it. The downside is they are EXPENSIVE but if you really rely on something starting when needed I'm a firm believer, plus they are essentially zero maintenance sans making sure the terminals stay clean (which because of very little venting they do).
I've got a relationship with our local BatteriesPlus thru our local fishing club and got to know the owner of the franchise, he's been a great guy (as have all his employees) to work with, the employees are well trained, and when I've had warranty issues they have taken care right away. Yes, all manufacturers have defects occasionally, it's how the retailer takes care that makes the difference. The other advantage to AGM is they are much more vibration tolerant.
Now, if you're just playing w/ this as a hobby, you might be better suited to a Walmart battery, they actually are very good for a conventional lead acid wet cell and priced extremely competitive. What ever you choose, try to buy the largest CCA that you can physically fit in the space correctly (meaning firmly attached and restrained from movement). There is no such thing as too big a battery (within reason) meaning don't let someone tell you that you should match what is there, if you can fit more CCA go for it, it means easier starting when cold. Your charging system will most likely charge anything you can fit in the space if it's in good shape.