I bought the original DH casing Assegai to put on my wife’s bike for bikepark use, on an 28mm internal Bontrager rim. Couldn’t get it on, no matter how hard I tried.
Sold it and got the Vigilante 29x2.6. Fit’s on the rim just fine, and in the first gen Fox 27.5 plus fork on that bike.
My guess would be that a big part is what casing size you like. WTB 2.6 is going to be much bigger than Maxxis 2.5, so if you like larger volume, WTB is the way to go, or vice versa.
Tire traction is also very dependent on conditions and riding style, so hard to make blanket statements about the grippiest tire.