Your body has three interfaces with the bike: Handlebars, saddle and pedals.
On bike models of the correct size, you should be able to get an identical fit on most any bike. You may even be able to go a size up or size down and get the exact same position.
To customize the position on the bike you're adjusting saddle height, saddle setback, and stem length and angle.
When a bike is the wrong size to achieve your desired fit you'd need to use an extreme stem, either very short or long, or of a large angle.
A bike that's too big will require a very short stem, and may not have enough standover clearance for you. A frame that's too small will require a long stem, and will usually have a much lower handlebar height requiring a lot of rise to the stem to get your ideal fit.
Comparing bikes of the same size (for argument's sake let's say Large, or 56 cm seat tube) you'll find some bikes will have longer or shorter top tubes, and some will have higher or lower stock handlebar height. These can both be accounted for by using different stems. You don't want to push things too far, stems range from 60 to 140mm, but 80-120 should probably be a more realistic range to shoot for. If you're using anything outside that range, I'd look at a different sized frame.
Cost can factor into this whole thing. If one model fits you nicely and won't require you to swap stems, saddles, handlebars etc etc. to get your desired fit, that can save you money, even if it costs a few bucks more than a competing model that will require more customization.
The problem is as a new road bike rider you're not going to be able to tell what's ideal for you to start out. Getting at least a 'freebie' bike fit from a shop when you buy a bike can get you started.
Go to a couple bike shops, and get them to size you up on some bikes. Get them to describe WHY they feel a certain size is right for you. The one which inspires the most confidence will probably also be able to get you pointed in the right direction in terms of fitting you properly.
Finding a shop you can trust to help you with this will be *FAR* more important than saving $50 or $100, or getting a free set of pedals thrown in with your purchase.
Honestly, mid range roadbikes (aluminum or carbon) from the various big-name manufacturers are all VERY competitive. Pick your budget, get a bike you're able to be fit comfortably on, and go ride the wheels off of it.