I own the Legacy MCX, Virtus, and Rattler along with various cal-x barrels for all of them. If you want to shoot 5.56, then I’d recommend the Virtus with 6.75” 300BO barrel. The Virtus gives you the best flexibility with barrel length/caliber changes. If all you’re going to shoot is 300blackout on the shortest possible barrel then the Rattler is hard to beat and 5.56 out of the 5.5” Rattler is a blast (literally).
I am leaning towards the Virtus PIstol in 300, I really like that the Virtus has so many available barrels lengths on 300 or 5.56, it appears to me it's more of the Swiss army knife of guns, I do wonder if Sig is about to release the next revision of the Virtus though.
I said the exact same thing when I bought my Legacy MCX. I’ve been lucky to be able to use my MCX lower across all three generations. I’m hoping the same is true for the next one and I can just buy the cal-x upper kits. Otherwise I may be selling off some of my current gear (shouldn’t be very difficult).
