let's do a side by side:
doesn't permanently modify freezer - collar wins
doesn't need extra space in back when opened - collar wins
amount of work/craftsmanship/tools required - tower wins
cooling - collar barely wins. collar w/o fan pretty much works with little foam. tower with no fan can be problematic
aesthetics - tie, i think faucets on a nice stained collar looks cooler than a tower.. but that's all opinion.
# of taps - collar wins, you're only limited by size of freezer really. for 4+ taps, you'd need two towers, or one big and very pricey one.
price - collar wins. faucets/shanks are much cheaper than tower w/ same # of faucets
CO2 tank inside or out? I wanted mine outside, so collar wins on that one too, if yours is inside (taking up precious keg space), it's a tie.
looks like collar wins to me.
that's what I did. double hinge design, 4 tap collar.