Welcome to the site !!!! Ramses has pretty much nailed it down on what to look for, I like the look of a box a arm over just tubing but that doesnt mean it is stronger. I have seen the XMF kits get BEAT on and havent seen any prob. So just get well known kit with Summer bros axles....STAY AWAY FROM KITS WITH GORILLAS ! Good luck on the search and let us know what you picked outWelcome to the Underground. Its good your doing your research on a quality kit before spending the big bucks. You definitely want to look at the materials being used on the arms themselves. Most reputable builders will use chromolly instead of DOM or mild steel. That alone will make a difference on the purchase price of the kit. Look at material thickness too. I like my Cognito kit because it uses heim joints instead of bushing and that lets me set my toe in and camber to my liking and style of driving. It uses Uniballs instead of ball joints. Uniballs take much greater abuse than a ball joint will. Some builders also use a heim joint inplace of a uniball.
Looks at what axles the builder uses too. I have had a lot of luck with Summers Brothers axles on stock CVs. I would stay away from the non name brand stuff and expecially Gorilla axles. I know too many people having bad luck with Gorillas popping out of the Differentials.
Most builders will also have a shock manufacturer that they already deal with. A good builder will have the shocks tuned to two seater and four seater applications so you can get the best set up out of the box. I personally like King and Fox shocks, but heard good things about Elkas and Walker Evans.
Also know your budget, this will be the ultimate deciding factor. Most long travel kits use a 6 inch or 6.5 inch stroke shocks. Some use a 8 inch stroke with shock towers to push the top of your shock out, these kits give you more suspension travel but are also a bit more pricey. Good luck on your search, a long travel is money well spent on a UTV.