I spoke with the FEO before applying for my FAC, and he suggested I should go for .17HMR.
However, in the event I disregarded his advice and got .22LR (BRNO Mk2).
My main reason was the cost of ammo - being completely new to rifle shooting I wanted to know that I could afford to practice properly until I got good at it!
Other things that put me off were the noise issue, potential problems in high winds, and meat damage. Whether or not these are genuine concerns I don't really know, because I've never even fired a HMR, but I hear them enough times to be convincing!
Now I love my .22LR. I have no desire to take really long range shots. A perfect summer evening involves lying behind a clump of nettles with the rifle on a bipod, about 60 yards from where the rabbits feed, and picking them off silently, one by one. Quite happy spending hours in the same spot, watching other wildlife come and go.
I've also learnt a lot about ballistics, trajectory etc, which perhaps wouldn't have been the case if I'd a bought a "point in right direction and pull trigger" type of rifle.
Above all, the .22LR has stood the test of time, it's the most popular round in the world, and in a fairly recent thread on here titled something like "if you could only have one gun in your cabinet, what would it be?", a significant majority said .22LR.
Also, if you need advice about anything to do with a .22LR, you can be sure to get a lot of sensible help off this forum. However, if you ask the same questions about HMR you'll get lots of vary varied replies, and probably a disagreement or two. A bit like this thread really!