How did you pick your Tri bike?

I'll admit.....I did it backwards and bought one before I got a fit.  I just built up a roady and had no intentions of buying, then went into a bike shop and saw it sitting there.  A left over Argon 18 E-80 built up with mostly ultegra.  Wife said "ok, you can get it, Happy Birthday".  I never do an impulse purchase of that magnitude but it was calling me.  LOL!  

Now, if you are at a place that has tons of bikes you can ride I would do that AFTER you get a it and know which bikes would be the best fit for you.  

Ditto. I had a Cervelo R3 road bike, and I knew I'd fit on a P2 from having tried it. So... $1800 instead of $2800 can't be beat. Plus it's red and black like my other bike, so all my accessories and clothing already matched

Bought my Felt S32, which was a screaming deal because it was a 2 yr old model just laying around.  They only had 2 Tri bikes in the shop as well so really hard to compare sizes, geometry, etc.  Also, I did next to 0 research.

I did my test rides with a cast on my left arm because of a recent mtn bike crash.  So my first time on a road bike, let alone a Tri bike with aerobars, was in a cast. The bike seemed to "Fit" just right.  After 6 years, that is still my one and only road/Tri bike and I have no intentions of upgrading anytime in the near future nor getting a professional "fit".   Maybe I was just lucky and this would have been the bike I would have naturally settled on if I did do comparisons + maybe the Bike shop guy was really good at doing my initial 20 min fit? 

After b@st@rdising a feew road bikes (the last one being a Softride), I finally had my position dialed, but hated the bike (for tri -- still have it as a roadie). So I searched high and low to find a bike that allowed that position and had good weight balance. Took along time, but eventually found one with a long-enough front center. Handles much better.

So... My choice was completely fit- and geometry-based.

I looked at the Kona bike count and saw that Cervelo dominates it year after year:

http://lavamagazine.com/features/the-2012-kona-bike-count/#axzz2Nqeoope4

So when my LBS was doing a great deal on last year's Cervelo P3, I snapped it up and have been very happy (note: the P3 gets a new color scheme every year but the bike itself has barely changed since 2006)

You really can't go wrong with Cervelo.

Ebay.

I knew the models/brands I was interested in, then I just waited for a killer deal.  I've bought two brand new bikes--last year's models--at deep discount (40% off) in December.  But I've bid on a few on Ebay as well.

knew my road bike size, saw my bike on craigslist, tested the bike, got semi fitted and decided that the bike would work for me when properly fitted and the price was right since the guy was dumping his equipment and I had been watching him drop his price over the course of 4 months. got mine for 1550 and brand new all the equipment he gave me was worth between 3200-3500.

I went by price, but it was the beginning of the off season, so I still made sure it fit.

Fit/positioning should trump any "deal" you get.  Beyond body dimensions, joint/muscular mobility is a factor as well, and a good fitter should see that.

Looks certainly helped, and I tend to be a rebel when it comes to brands.  I'd rather be out there on a more obscure bike, than going with the crowd.