I have the Sigma 300 f2.8.
I’m very happy with it. It’s arguably the best lens that Sigma make.
It does not have IS/OS/VR that perhaps the Canon or Nikon 300 2.8’s have, but its lighter and very sharp and fast. Oh and not to mention, half the price of the Canon and a third of the price of the Nikon!
Would I take the Canon over the Sigma if they were the same price? Sure, but at 50% of the cost the Sigma 300 wins hands down.
I also have a 70-200 f2.8L But for wildlife the Sigma 300 f2.8 is always on one of my bodies as my primary lens.
If you want flexibility, why not consider the Sigma 120-300 f2.8? It’s said to be very close to the 300 prime in terms of IQ, and its similarly priced. (my preference would still be the 300 prime lens.)