Road bike or tri bike for ironman?

You're going to get a ton of varying answers here.  But I absolutly love my tri bike.  And I know you are doing IMFL which is FLAT which is best suited by a tri bike.  I am more comfortable on my tri bike, but i know there are going to be lots of people on here throw out the "fit" issue being the most important.  Which is true, but i am fit well on both and i still am more comfortable on my tri bike.

I am one of the rare people who like a road bike better. I do find the road bike more comfortable and have never been able to find complete comfort in the aero position. I have been fit on both bikes, but I still just find the road bike more comfortable. I am willing to give up a small bit of speed for the comfort.

If you have a decent fit and lots of time training on it, tri bike.

It may just be me, but I would make the choice depending on how much I think I would be able to stay in earo.

If it's a flat to rolling course, the tri bike.  If there is a lot of climbing, the road bike.

If you are not going to ride in earo, you just lost all of the advantage a tri bike gives you.  For me, the road bike gives me more leverage for hard climbs and out of the saddle efforts.

But I miss my tri bike on long rides becuase I like to take some pressure off my arms and hands and get in earo.

I prefer a road bike... the function and safety is higher when training on a road bike and handling is better as well.  Brakes, gears and hoods all in the same place.  If you're racing for the podium or looking to fit in with the majority of the riders in a Ironman ride an aero/tri bike - part of the fun - oh and buy a Cervelo - that's the most common bike too!  I'm not fast enough to care and when I train I'll take function over form everytime.  Since I train on a road bike - I'll use the road bike in the event.  It's been said... aero is free speed.  Free my a$$.  It's expensive speed and I'll still not be anywhere close to the podium either way... unless I use a taser and take it by force.  By the way... I've trained on both and can afford both I suppose... I still like the road bike better.  Don't care for the aero position.   

If you are properly fit then your tri bike in aero should be comfortable. Not to mention the fact that you should put in enough miles that your body adapts to the aero position.

In my area (as with many areas) I see a tremendous amount of people using aero bikes and aero bars who would be best served on a road bike for function, safety, versatility and lack of expense (more bikes to choose from when buying used and generally more lower priced new options as well).  Get fit on a bike - any bike - and then worry about a TT bike if and when you squeeze the upper limits of your fitness and you're still interested in racing.  Recommending an aero bike to beginners isn't necessarily solid advice.  It's very restrictive in so many ways and creates more obstacles to getting into this expensive sport.  Personally, I've been fit and can fit people to triathlon bikes and still enjoy my road bike more for the reasons mentioned above.  In addition, group riding is much easier as well creating a social network increasing the likelyhood of adherence. Bottom line... keeping things simple will help adherence for those starting out and all these aero items to shave time should be held out for another crowd and /or at a later date.  

And if you are fitted properly in that position, then fine.

I'd go aero and save the energy - tri bike.