I’m about the same height as you 5’10.5″ and went with the 19″ as it had the same geometry as my Kona SS 29er. It is a perfect fit. I posted a thread with the same question and answers fell into two camps. If you like a small bike then the 17.5 may be better. I wanted pretty much what I had before with front suspension and smaller wheels.
It’s only my second mountain bike, although my son has a Giant Trance which I’ve ridden too. Compared with FS, it is very fast climbing, and I think the hub helps with shifting, it’s firm at the rear (hence carbon seatpost) and is a nice ride. For the money, you can’t go wrong in my opinion.
And now for the good bit… Rode back to the car park covered in mud, rinsed down the downtube and put it on the Thule 591 rack and drove home. In the time it took to stop, and mount, the guy with a FS next to me hadn’t finished cleaning it. Yes it’s covered in dried mud now, but I won’t bother cleaning it, I may lube the chain before the next ride. But I know its performance won’t be impinged. It’s a great all weather bike!
If you are near Swinley, you are welcome to test ride it.