VM aren't the only network with problems, but they are the one having apparently persistent and widespread problems with upload speeds and latency, due to lockdown. That's down to the technology that underlies cable internet, so there's a fair chance it will resolve when the world returns to some form of normality (meaning schools open, and a lot less working from home by office workers).
If you're not prepared to wait and hope, then performance of Openreach ISPs is generally better than a VM area suffering over-utilisation (many VM customers aren't affected - my area is performing normally), but it will be slower, and if the ISP has over-subscribed the backhaul capacity they've bought there can still be problems. Expect the cheapskate ISPs like Talktalk or Voda to be suspects for that. Openreach themselves are quite carefull to avoid over-subscribing their bit of the network, due to better regulation than VM, but that's not a guarantee.
If you are planning on leaving, I'd suggest you consider whether you want cheap and cheerless (C&C) which can often work out OK, so long as nothing goes wrong, or whether you'll pay a bit more for a different league to tech support and customer service. If you want C&C, then Sky, Plusnet, Talktalk or Vodafone may have attractive deals, although they offer the same skanky offshore customer service as VM. If you're willing to pay a few bob more a month, then your shortlist is AAISP, Aquiss, CIX, IDnet, uno, or Zen Internet. All have UK customer support, an excellent reputation for support and service, and are far better than the big ISPs at getting the best out of Openreach. They'll also have competent provisioning staff who can probably tell you whether there's any contention problems in your area, and what sort of speeds they can deliver. I've had dealings with Zen, on behalf of elderly relatives, and I've always been impressed with their service.
At say £40 a month, and an 18 month contract from the C&C ISPs, probably 12 months with the smaller ones, you're thinking about a £500-700 commitment, so put as much effort into your research and thinking as if you were buying a similarly priced piece of equipment. Make a shortlist of companies you'd consider, check out their customer reviews on Trustpilot and ISPReview, and choose whatever suits your budget and needs.
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