This is what I've switched to after suffering with a shit ADSL connection for far too long (and no hope of fibre at my address).
I went for a Huawei b535 router (£90 with a strong resale value) and £35 a month Giffgaff sim. It's worth doing speed tests on a number of networks and in different rooms before you decide which provider to go with. I get strong 4g signal on my phone with Three but the speed is only 15-20 mb/s, on Giffgaff (O2) we're getting 80mb/s download, 20mb/s upload.
Suffered 2 days of slower speeds last month due to O2 working on a nearby mast but other than that it's been stable.