You are correct, there is no "right" answer to this question. The number of variables is just huge, and tech specs do not always translate into "works better" in the real world for what you use the phone for.
I've just been in this precise situation in my own household. I have a Galaxy S7, which I like, but the screen is getting too small for me. My partner had no smartphone and finally broke down and said he wanted one because he wants to be able to use Waze. Our service is on T-Mobile, so an unlocked GSM phone is what we were looking for.
I went through three different models: BLU Vivo XL3 Plus, Dougee Y6 Max, and Redmi 5 Plus before settling on the last one. The first was great but for one major thing: it could not make outgoing calls. It would put itself into its own Do Not Disturb mode as soon as you tried to place an outgoing call. This happened on *two* of these devices (I thought the first had to be some sort of fluke) and even their technical support (which was great, I wish the device had been) folks said something was wrong with the units after going through a long and through diagnostic process.
The Dougee Y6 Max, which has a huge 6.5" screen, would have absolutely been a keeper except for a deal breaker: The GPS in them is, how shall I put this delicately, completely unusable. How I missed that in the reviews for the device I do not know.
The Redmi 5 Plus looks and feels like a flagship phone, though the tech specs aren't the highest. That being said, it is a way more than adequate performer in day to day use for all purposes and at $189 new the price is hard to beat for the feature set.
I just decided to do my own experimenting with a flagship from 2016 from a Japanese maker, Freetel, that never really got traction here in the USA. Someone in Texas must have cornered the market on the remaining Samurai Kiwami flagships they were marketing here and is selling them via multiple venues (eBay and WalMart.com included) for under $100 [the cheapest site being WalMart.com at $91.99]. It's hard to beat the specs on that device at anywhere near to that price, but the drawback is that it comes with Android 5.1 and the only update is to Android 6.0.
This is really all a game, and it can be an extremely exhausting one, at that.