Honestly i think all three of the standard ar big bores are pretty similar.
The .450 has a better selection of lighter bullets, and the .50 has an extra .5 cal of initial dia. So you really have to weigh the advantages of each and your expected uses.
My guns primarily a hunting rifle, which ive shot stuff as large as feral cows with. So the .458 was a better choice for me as its particular advantages are head spacing on the shoulder. And wider range of mid to heavy weight bullets, being the only rifle cal of the three.
My gun is a 16" (pistol length ars arnt legal here) and delivers 1900fps with 300grn bullets and 1650 with 405s. Im not sure how much velocity would drop in 4 inces less barrel, not a whole lot id think.
I think the advantages the big bore ars have over an SBS is usable magazine capacity (box mag Shottys not included) , and better bullet selection. While i cant attest to it personally, having never shot a short barreled, or rifled shotty, id bet velocity and accuracy are better from the BB Ars with similar weight projectiles.
Personally something specific to home defense id opt for a pump sbs, but for general use i think the advantage goes to the BB ars.