I've been pretty lucky with landlords. My old flat in Hull was initially managed by a letting agency run by two women, one of whom was grumpy but formidably efficient and the other very nice but formidably inefficient. Subsequently the landlord took over direct management of the place and he was pretty good - sometimes a bit slow about getting non-essential repairs done, but when anything was urgent it was done pronto and he was perfectly pleasant to deal with.
My best landlords were the couple who owned my flat in Charlton. I didn't even meet them until just before I moved out, after five years. They were always nice to deal with on the phone, though, very quick to get repairs done and very conscientious about things like gas safety inspections. And I was still paying the same rent when I left as I had at the start, which must be practically unheard of in London. Unfortunately I left that flat to move to a place owned by the only dubious landlord I've had. He wasn't nasty as such; just a skinflint who did everything on the cheap and then wondered why it didn't last. And he didn't clean the house properly before we moved in, despite promising to do so, meaning that I had to spend a day up to my elbows in bleach before the kitchen was clean enough to use. I thought he'd find an excuse not to return our deposits when we left a year later, especially since I'd smoked in my room, but perhaps we underestimated him a little, because we did get them back.
My current landlord is a nice bloke. Not tbh the fastest to get things done, but anything urgent has been seen to quickly, and he's always pleasant to deal with. A couple of months after I moved in I let him come in to measure up for a new gutter at the back whilst I was in London, and got back to find a bottle of wine on the kitchen table and a note thanking me for letting him in and saying, 'you have made the house look really lovely.' When I told him I'd bought a place and would be giving him notice at some point before long he just said, 'I'll be sorry to see you go.'
Some landlords are bastards and the law is unfortunately on their side, and at the bottom of the market, especially, you get some exploitative scumbags. It's probably easier for landlords to get away with being bastards in London, too, because there's so much demand for housing that they can always get another tenant in, no matter how much they stick the rent up. With one exception, though, my experience in both Hull and London has been that if you're reasonable with them, they'll be reasonable back. It's not in their interest to upset someone who's paying the rent on time and looking after the place, because then they'll up sticks and go, and leave you with the cost of finding someone else and/or the place standing empty and earning nothing for a while.