You should buy the bike where you are most comfortable on.
Later on, you want to do more training. Most of us do the longer training distances on normal bikes. A TT (time trial) bike is a possibility but they cost quite a bit.
A "normal" racing bike is far cheaper and easier for maintenance (I think). that way you can learn some bike mechanic skills, those will save you some money in the future. The sport/dicipline is expensive enough already
A normal racing bike with a time trial steer/handlebar setup will get you a long way.
Just my 0.02 €