If it was me...
I would start with the easily accessable 80 proof bourbons.Again,if it was me,I would start with Jim Beam White Label.I would do this for 3 reasons:
1.It's fairly reasonable in the price area
2.It's not offensive
and most importantly,
3.It has a very simple flavour profile
Basically,what you get with Beam is a little caramel,a little vanilla,a little corn sweetness,a little oak,a little barrel char,and occassionally,there's a citrusy thing going on.Most bourbons have all those in varying quantities,with different levels of nuance,as you work your way up.
Then I might try Wild Turkey 80...It's a bit different than Beam,and you'll notice the difference,but it's only a slight difference.
Then I might try Jack Daniels Old No.7...I don't find that stuff terribly appealing,and it's not exactly bourbon,but it would be worth the effort just to see the difference.
Mike's right,try Four Roses Yellow Label...For an 80 Proofer it has alot of nuance and flavour.
Now,what I do is I always go back to Beam to get that simple flavour profile back in my mind.Then I might try Jim Beam Black in a side by side with standard Beam...
Then I would try the 90 proofers like Makers Mark,Woodford Reserve,Four Roses Small Batch,Bulleit,Buffalo Trace,etc...Even George Dickel No.12...
Another thing about Makers Mark...Occassionally,I have got a bad bottle of the stuff.I had one last Spring that tasted literally like soot!And I wonder if you've got a bad bottle because Makers is a fairly sweet,completely agreeable bourbon?