Owning your own home

As @Howard mentioned this is indeed my area of expertise but to be honest everyone else here has covered it nicely! Unless you have the means of installing the collector yourself I would be quite content with an ASHP these days though if you have access to a digger and a few helpful mates it's not really a terribly tricky job to do a collector...
The most important thing to note is to make sure you have a buffer tank, insist on this and if the installer says it's not necessary I'd look elsewhere. As a general rule of thumb, the bigger the buffer the better... even with inverter driven HPs, a buffer will reduce starts of the compressor and ensure there is sufficient volume in the system to lose the heat from the compressor after runs which will increase longevity.

If UFH is in anyway conceivable I'd say do it. As mentioned before there are lots of ways to install it nowadays with cutting machines etc. and aside from reduced running costs the comfort is just another level compared to radiators.

If you have someone local to fit it and the budget suits I'd recommend Viessmann, they're the best quality domestic machines out there at the moment, I put one in my place.

Any other questions fire ahead and I'll do my best to help!