Ah, we've all been there. Before you know it, you'll have strong opinions on what OS is best for everyone.
These days, you really cannot go wrong. There are plusses and minuses, but pretty much any phone you get will do what you need.
First, I'd decide which carrier(s) you're willing to use. That will reduce the models of phones you can get.
Second, I'd decide if you want to go off-contract (buy outright) or get a phone and sign a multi-year contract. That will also affect your decision.
Third, I'd go into any store that sells phones and hold a few to see what size feels best for you. Some like big screens, others like easier-to-hold phones, and that might help you decide. it doesn't matter which store you choose - you're there to decide basics like size.
Fourth, decide on a budget. If you want to go off-contract and only have $200, you're not going to get a flagship phone from anyone, for example.
Finally, try out some of the specific phones within your budget from your carrier by going to that carrier's stores (or places that sell for that carrier) and play with each phone you'd consider for a while (more than 10 seconds, for example - spend a few minutes with each).
Once you've done all that, it's really up to you. Don't be weighed down by all the fans of all the various OSs here. Fundamentally, the phones
all will do what you want. Choose the one you like the most that fits your budget.