I think the first step is to decide what kind of volume of beer (# of kegs and taps for simultaneous availability) you need to manage. That will drive the size of the unit. Then some choices on how you will use it. If it's a showpiece for your family and friends, then that can drive the type of tower, faucets, other bling. I personally just wanted to have cold storage for cold crashing, carbonation and be able to have homebrew and seltzer on tap easily. I did not want to spend $450-550 for a store-bought unit. With a little research and patience, I found a nice used wine refrigerator on craigslist for $80 that had a real compressor (not thermo-electric) would fit a 5 and 2.5 gal corny. I added a $30 Inkbirk supplemental temperature controller for better control. I was going to cut a hole in the top and add a tower faucet and the necessary anti-foam fan but decided that just having a picnic tap was fine and less mess to manage and clean.
I suppose if I had not had the gas bottle, regulator, other fittings and wanted a dual tap tower, then finding a new kegerator ready to go (maybe on sale these days) would have been a compelling low hassle option for a little more money.