I am just over 4 years into my S7.
I used to have an S4 and an iphone at the same time. Personal and business. I did that so I could compare the 2. The S7 was hands down, better in every way. I gave away the iphone, such a horribly proprietary thing, shelved the S4 and bought the S7. Best move I ever made. I eventually gave away the S4 to a member here in need.
I am only now, 4 years later, having battery issues with the S7. Unfortunate it cannot be easily swapped, but the neither can the iphone. I put a battery in my iphone 4 myself. It was a real chore. Did my homework on putting a battery in my S7 and decided to replace the phone instead. They make battery replacement ridiculously difficult. The S4 was easy, pop the back off with your thumb, pull the battery, done.
Couple weeks ago I ordered a new S21, basic model. 256gb but no card slot like my S7. They have 128 or 256gb. Oh well... Samsung got cheapo like Apple and don't supply a charger. A major beef with me, because the newer phones use USB-C. My S7 charger won't work. Yours won't either.
Backup is super easy on Android. I plugged my phone into my laptop, it showed up in Windows Explorer, drag, drop, copy to backup directory, done. With Apple you have to use their stupid itunes junk. A real pain, and your files are encrypted to Apple format. You can't read them.
As for the 2 for 1 deals, it seems they gave done away with all those. And it seems that gone are the sign up for 2 years deals and get a free phone. I always buy my phones outright so I am in the drivers seat with carriers. No contract, if I find a better deal away I go.
I just dumped Telus at 85 a month for unlimited calling & text, 2.5 gigs data, and went to Koodo, $45 a month, unlimited calling and text, but with 6 gigs data.
Deals are there at various times if you watch. With no contract, you are free to switch.
Phones are so expensive now compared to a few years ago. They used to be willing to give you anything to get your business. Free phones all the way. Not any more.
I checked out their "deals" Pay 300 and something down, sign up for the 2 year program and pay 30 a month extra for your phone. I did the math and the price is to the penny the same as if you buy it outright. Whoopee... such a bargain...
I can't tell you how the S21 is, I'm still waiting for it, and the goofs at BestBuy can't tell me when it's coming. That's another story...
As for the "best" to buy, that a matter of preference. I spent gobs of time researching Android devices. Don't want an iphone so that narrowed it down. My reason for sticking with Samsung S series is because of how good my S7 is. It has been excellent. Wasn't the same after I dropped it and smashed the screen though. That's not the phones fault though.
The S21 is 5G. But it works fine on non 5G networks, backwards compatible. Koodo doesn't have 5G. I really don't care. Can I make calls? Yes. Ok, fine for me.
I suggest you do all your research online. I did. Found the best phone for me and ordered one. Then I found the best deal on a carrier and went for it. I will be paying half of what I was before. Do some math, the phone will pay for itself in the plan savings, and then some.