I am currently with TalkTalk and am scoping out different ISPs as my contract is up at the end of March. I have frankly had enough with the current speeds I am getting (70 Megabits per second on FTTC)
FTTP from Openreach isn't available yet and on the Openreach site, it states that FTTP will be built in my area between April 2022 and April 2025, so my only option is Virgin Media which has the Gigabit package. Altnet ISPs will not touch my with a bargepole.
You won't get a reliable answer on what your individual connection will turn out to be like because it will be your own individual connection i.e. if you are relying on old/existing VM cabling to use to join VM then that could influence your individual connection, for example.
If you need a new connection/cable, then have a look at some of the issues which have cropped up in the 'Quick Start' forum on difficulties and long delays getting a new cable installed by VM. These may be an exception rather than a norm but you should factor in the possibility.
If you are able to, you should overlap your TalkTalk connection with any new VM service. That way you can avoid any interruptions to service and, if VM turns out to be no good for you, you haven't given up on TalkTalk.
I have been with VM/NTL for 20 years. The last time I had a significant issue with broadband with more than 8 years ago (which was actually an issue with over-utilisation in the area). VM are supposed to have stopped allowing new connections to over-subscribed areas. How reliable that is, I couldn't say.
From my own experience, there has been less to worry about on the technical side but issues with the company typically relate to their administrative and customer service operations. These have always been poor but, in recent times, VM have effectively made themselves non-contactable. Overseas phone support is very limited in its abilities and often achieving simple tasks can take huge amounts of time simply in making contact with VM.
I have now just moved to a BT FTTP connection which became available a couple of years ago and it is very good indeed and obviously built on brand new infrastructure as opposed to the possibility that a VM connection may be relying on 20+ year old infrastructure from the early days of cable TV.
If you opt to try VM with a view to leaving in 14 days cooling off, be aware that getting in touch with VM to make that cancellation and have it put through reliably may be extremely difficult and time consuming with the way VM is running its customer services and call centres at present.
This forum is the most reliable way to get things done but, unfortunately, the forum team generally aren't able to deal with package and payment issues.
Nothing to say you shouldn't give VM a go but be aware of some of the above issues before deciding to take the plunge and factor those in to the decision making process.