The only wheel size combo that has not tried to kill you. Yet.
I had to do some thinking on that claim. My worst crash was probably my 2014 Lynx crash - but I have no recollection of that. My face remembers however. That was on my Knolly Endorphin (26er).
I really only had a couple of minor crashes on the Tracer (full 27.5), including a boxer break on my left hand NOT caused by hitting the ground. That was a crash on 5-Oaks. I can't recall any other crashes. I believe my best DH times on local trails were probably achieved on that bike, but I wasn't doing STRAVA then, so I'll never know.
My short-lived Pivot Firebird (29er) never threw me to the ground, but I didn't like it very much. I did have at least one very fast run down The Luge on it, but again, not documented, so who knows?
@Runs with Scissors was with me. Way, way, way way behind somewhere.
Then there was the Megatower (full 29) that threw me to the ground very roughly at least 3 times in its short time in my possession, including an airlift off Rock-It. We did not get along. That was one unforgiving beast!
The Revel Rail, in its full 27.5 or in its Mullet iteration has been highly dependable and friendly to me. I slid out on it once on Lizard, but no injuries or even scrapes from that one. I set some pretty solid times in its mullet form. Most of my documented STRAVA records down were in 2021 on the mullet version of the Rail.
My full 29er Yeti SB 130 LR is a great bike, but I have not really put it to the test climbing chunk or descending anything harder than Rock-It or Luge. I did ride it on T and A once, but my hip was so bad then I didn't want to risk an "unplanned dismount" so I walked the crux and the last drop. Maybe the SB 140 is my true goldilocks do-everything bike - since that bike allegedly fixed some of the negative characteristics of the 130.
So for purposes of this thread for the original poster posing the question, I still stand behind my assessment that a full 29er is the best option.