For the last five years I’ve been using a FrSky Taranis X9D.
You get a lot of radio for the money.
It’s probably the most popular radio in use these days so there’s a very large helpful community of users.
The protocol used is very robust and near impervious to interference. The only other system I would say is equal or better is that used by Futaba. But a Futaba radio with the same features will be four or five times the cost of the Taranis.
The receivers are relatively cheap but excellent quality. As an example I’m currently using the XSR receiver in all my SBUS capable models. This is a 16channel, full range, diversity receiver with full telemetry support. It’s about as big as my thumbnail and is about $20.
It’s fairly easy to modify but even in stock form it has a proven range of up to at least 10km.
You could also look at the FrSky QX7. This is essentially the same as the Taranis but with a few less switches and no sliders, and the case is made from cheaper materials. If you shop around you might be able to pick one up for under £100. It supports the same receivers as the bigger X9D and has the same module bay so you can run other systems. E.g. TBS Crossfire, EZEe UHF, even Spektrum DSM2/DSMX though personally I’d only trust Spektrum with small park flyers at close range.
If you check YouTube you’ll find literally 100’s of reviews and tutorials for both the X9D and QX7.