I have both, and while the newer .22mag ammo narrows the gap somewhat if your buying it as a rabbit rifle I would say 17hmr all the way.
As has been said, if you also want to use the rifle for goats/wallabies then .22mag.
17hmr suppresses just fine and won't lose any speed-hell mine gains a very small amount.
17hmr is also less of a ricochet risk than any .22
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