If you go in with preconceptions of clubs you like you'll likely give yourself reasons why they're preferable even though they may not be. I know this through personal experience when I went to a Mizuno DNA fitting and had the idea that I liked the MP-59's which Luke Donald was playing at the time, although that wasn't the reason I liked them. I then got fitted and the suggested club at the time was the JPX 800 to suit my 22 CONGU handicap. I persuaded myself that I would practice longer, more often and be better off with the 59's as they'd punish me more for bad mechanics so I ended up with those, albeit with correctly fitted shafts.
After a year I decided they were far too punishing and I traded them in for some JPX 825 Pro's which were far more suited to my skill level and practice regime.
I'd approach it by telling an experienced fitter about your game, about your practice sessions and about manufacturers you do/don't like the look of and let them make suggestions to you.