Get the bike that has the Best Fit (feel) to your body.

Try some Long Test rides.

Or buy a used bike and learn what works best for you.

Craigslist is good for that in most areas..

I started with a $15 craigslist bike.

Rode it 1500 miles before buying a new one.

The new one had a perfect fit, gearing, and feel for me.

Rode it 39,000 miles.