How much variation is your team possibly accepting? Is your team pretty much going to do a WCD for any game, or are they open to somewhat different chassis designs, and are you willing to consider them? (There are teams which do quite well with the “single drive” paradigm, including some repeating world champs, changing only wheels, gear ratios, and (when the rules indicate) number of motors each year.)
If your team is fairly locked in, learn all you can about the options which ARE under consideration. Download JVN’s spreadsheet and play with the drive train pages until you don’t have to think about how to enter the data, just what it is that you want to make happen. Do searches on CD and perhaps the wider world on the parts you typically use, and become familiar with the foibles and workarounds people have developed. In short, become an expert on your team’s drive system, so that you can smartly suggest appropriate wheels, gear ratios, and such.
If your team is more flexible, learn about the different drive systems which have been used in FRC, and their strengths and weaknesses. Find case studies of teams who have posted their engineering notebooks or build season notes or whatever they call it who’ve used these systems, so that you can intelligently guide your team to the correct choice. There are a variety of overviews of drive systems, mine (no claims it’s the best, but it’ll get you familiar with the popular drives and terms to search to learn more) is in the second and third documents here. Edit: Oh, yes, do the same with JVN’s spreadsheet in this case, too!
If your team is somewhere in between, do some of each!
And of course, remember what your team has been through the past few years. Looking stuff up is great, but if you aren’t familiar with what has and has not worked for your team, you aren’t going to be able to make your case (whatever it is) convincingly with your team. If your team has historical notebooks, read them (especially the chassis parts). If not, find some time to chat with the mentors about the history of your team’s chassis and how you got where you are now.
Another Edit: And +1 to CalTran and Billfred’s advice; intended as a supplement, not a replacement. We have used the AM14U2 the past three years (not much different than the U3) and have already purchased two U3 chassis which we’re 90+% likely to use next year. We’ve never built a KoP stock, but we’ve customized it 4 of our 6 years, and are quite happy with the results. In 2015 we pimped it into an H drive, in 2016 we had 10 wheels of 3 different types, overlapping in different planes, and last year we went 4 wheels, chopping off the front 3/8 of the chassis, and substituting U3 wheels.