Any of these worth checking out?

I'm looking for a first road bike, but want something that will last and I won't "grow out of" really quickly. I did my first sprint triathlon this year and want to do some more races next year (sprint or maybe Olympic distance, no long ones), but comfort for training and general recreational/fitness riding is more important to me than marginal increases in speed. I would like to stay below $750, but might go a little higher if it will get me significantly more life, better components, etc. These are just what I have found on Marketplace so far.

Bike 1: 2015 Giant Defy Aluxx 1, low mileage, shimano 105. No updates or modifications, but says it had "full service this summer."

Bike 2: same as above, but unknown history prior to current owner. Farther away, cheaper, but maybe could be used to bargain down the other one a bit.

Bike 3: 2017 Cannondale Synapse, Shimano 105 disc. Asking $500. Current owner rode once, previous history unknown.

Any of these worth checking out? Should I just keep watching the used market, looking for something newer? Would it be worth trying to bump the budget for a new bike with, say, Tiagra (or even Sora?) and hydraulic disc? I went to 3 LBS today and test rode a Trek Domane, Cannondale Synapse, and Giant…something (they didn't have Contend in stock, but said the geometry would be very similar) that, of course have the latest tech for their price range. Also planning to try an Allez, but the shop didn't have it built yet.