Either will work fine.
Given that you are coming from a flip phone, I doubt you have any brand loyalty/compatibility to satisfy.
You also likely aren't going to need to worry much about which apps are compatible (all the basic ones have versions for either system).
Big differentiation for your consideration is cost. You can get a base model that will be light years more capable than your flip phone if just buying a low to mid range Android. iphone is always going to be more expensive until you get into the high end android phones...but you don't need high end. You should be able to get a decent phone under $200.