I have a Ar20 and it is a very accurate and good rifle, however, it is a bit front heavy and the cocking is a bit tricky.
The MPR is a great rifle and was used by the 2010 world champion Mark Wall,
The HW101, in my opinion is the best of the three, I had one on test and it was extreamly accurate and out of the three, it is the only one that is regulated.
If you pop along to Maldon AGC, I will brig the AR20 for you to try and I know a few people with MPR's and Hw101's
All the best
PS, check out the new edition of Airgunner (out in a few days), there is a review of the HW101 for HFT
Somehow I made TEAM ENGLAND 2012 and 2013
Illiterate writer for AirGunner
The real Kung Foo Panda.