OR Fibre First are in Alton and Basingstoke so hopefully your long term prognosis will be good.
As for 4G you may like to read through this if not already
Most of us are lucky enough to live within reach of a fairly strong UK mobile broadband (3G, 4G or 5G) network signal but that isn't true everywhere, particula
www.ispreview.co.uk
Coverage maps lie and there is a lot of work going on in the mobile infrastructure. The only way to be certain is yes to test but that can get expensive. From what I can ascertain:
Vodafone coverage good (outdoor) but Band 20
EE coverage good (outdoor) but only Band 3
THREE coverage patchy Band 3
O2 coverage patchy Band 20.
So I personally would start with EE/THREE. Try and borrow (or Pay as You Go) to try both in the Loft. If the signal is as good as the maps show you may not actually need an external antenna. Many on these pages have found that a loft located 4G router with paddles is good enough. I personally favour a 4G router in the loft cabled down to the house network with PoE Injector/Splitters providing power for the 4G. But you will find a host of solutions discussed on this site.
I wouldn't spend a fortune as you will only probably get a moderate speed but no reason why you shouldn't get above 30/15.
If you are considering turnkey providers then I would compare them carefully with current offers from the main mobile providers (upfront, monthly, router quality, mobile provider, locked etc). Many independent Aerial suppliers (TV/Satellite) can offer 4G antenna services if that is an issue.