I have a 16" barrel tikka 223, 550-ish rounds thru it unsuppressed, og-6s waiting on the man to do his thing...having that experience, from purely a muzzle blast perspective, if I couldnt shoot suppressed I might do 20 in.
Benefits to 16 in - very compact and handy, steady in various positions. The stuff about shorter heavier barrels folks are talking about above is noticeable, it seems more steady.
No experience with a 20 in Tikka 223, but in general a 20in bare muzzle is not unwieldy to me.
This will be my favorite rifle once suppressed, basically already is. Factory wood stock.