I vote for the Silencerco Sparrow.
Easy disassembly
can be used with .22lr, 22 mag, 22 wmr, 17hmr, all the way up to 5.7x28!
very small ~1"ø, 5" long
full auto rated,
o-rings for better seal
~41db reduction
$369 is about the cheapest I've seen, though.