There is plenty of good advice on this thread. If possible at some point get professional training on pistol handling...either IPSC or Self-defense/combat training where you have an expert observe and ensure you are applying fundamentals correctly...this will improve your ability to handle ANY pistol, even ones that don't fit you ideally. It also saves you money in ammo trying to learn things on your own. However....
1. Do handle and if possible shoot as many pistols as you can to see what you do best with. If unable to actually shoot one, dry fire one and pick the one that the sight picture does not shift much as you pull the trigger. Depending on your hand size, the size of grip, length of trigger reach CAN affect how efficiently and easy you can pull the trigger and maintain alignment.
2. Take courses or participate in competitions where you learn to use your pistol under time pressure and duress, this will let you know what platforms are more efficient FOR YOU. No one else can accurately predict what is best for you.
3. Comfortable 'fit' of the gun may not mean that you can efficiently use it, only live fire and various drills can reveal that. In my case over time I realized I did much better with singlestack guns, and with short 1911 triggers instead of the long triggers I originally put in my 1911's....due to my hand size.
4. As you become more experienced you will naturally discover that the original choice might not be the most efficient one for your needs, that's ok and most of us have taken a journey to discover what works best for us. Enjoy the journey.
5. Please note that will proper training, you should be able to handle almost any handgun, regardless of how ideally it fits. When I say you find a platform that fits you better I mean it will be a bit more accurate than others, or you are able to draw it a little faster, and align the sights a bit easier than other platforms. Depending on your use for the gun, these tiny gains might be very important. In my case, I can shoot double stack guns but the smaller grip of singlestacks work better for me. Some platforms are just more accurate....my P239 can match or beat the accuracy (in my hands) of double stack polymer guns or even custom 1911's despite it having a DA/SA trigger...(and yes I fire it in DA for first shot and decock before holstering). I can still shoot guns that "don't fit me" but performance will be a bit worse than with guns that "fit me".
6. If you end up with a number of pistols, do take time and practice with all of them. Having a gun with a slightly different trigger reach/grip size than your preferred gun makes you focus on fundamentals which improves your shooting not only with the "ill fitting gun" but also your preferred gun. For example, practicing DA/SA shooting with my P239 really helps me focus on trigger control even though I prefer striker or SAO guns.
7. On some platforms (1911 for instance) you can change grip thickness/trigger length, or you can change grip inserts on polymer guns to change grip size. Do actually fire your pistol in different configurations to see if certain modifications fit you better (this is more important if your hands are smaller/bigger than average). For most people this won't be significant.