"Freemium" games are games where you get them for free, but with heavy focus on in-game purchases. It is common to get slowly bent over a barrel where you have to pay money to make your previous investments worthwhile and so on. "Premium", in this case, simply means a single purchase for unlimited playtime. It does not exclude DLC. Which is better for mobile and which for PC? Personally I'm a premium type.
I prefer premium for both. I like getting the entire game (excluding DLC) without having to go back and buy more stuff. I find it more convenient. I also research and usually play games before even considering to spend any money on them so I don't have to worry about buying something I'll regret later.
For mobile I like Freemium. Im cheep like that, and if I can get the same things without spending money, then Ill take it. Its more difficult, but I saved myself a buck or two.
I don't mind freemium if it is just cosmetic items but when it is new guns and stuff that otherwise you have to play for days to unlock just 1 it ends up making the game pay to win if the unlocks are even a little bit better it makes the game unfair to people who don't spend money in game.
You haven't mentioned subscription based which I think is one of the best methods because you only pay for how long you play so you can just try the game and not have to pay all in one go but the downside with this is that it can generally cost you more then a game would cost if you play it for longer then a year or so depending on the charge so premium can be better.
They all have pros and cons so it all depends on the situation IMO.
Usually, Premium is better. Unless the Devs do it as a hobby, and run on donations and/or ads, I prefer to pay once and be in. Possibly with a nominal recurring fee if the game needs upkeep (something
Premium is better, I like to just pay the fee and not have to pay again. Although if it's cosmetic things (like hats for instance) then I'd be fine about it.
