IA10 is probably cheapest for Di2, or you could get the IA14 and spend a lot less if you don't require electronic gears.
The IAx bikes come with the Bayonet 3 cockpit which looks to be a great choice, decent aerodynamics and loads of adjustability. For high yaw it should be the fastest of the 3 all else being equal.
The Felt also has the integrated bento box which was originally a selling point for me. However, the more I've found out about it the less I like it. It seems rather small, tricky to access and prone to the cover falling off.
It's a little heavy too but that's not a huge concern for Tri. Everything else about the bike looks pretty good to me.
- Aerodynamically good
- Spec is good assuming you'll use the original wheels for training
- Adjustability for fit is good except that the stem probably can't be replaced or flipped. (I believe it's delivered with the steerer cut for the bespoke stem with a short clamp area and no stem spacers)
- Mounting options for water bottles/draft box etc are better than usual (although a top tube mount in place of the integrated bento would suit me even better!)
- Some integration but shouldn't make it too difficult to work on
I know a lot less about the other two.
Hope this helps