I'm not as familiar with the work of Anthony Rapp (he's joining the franchise in the role of Lt. Stamets according to IMDB.com) (picture above right). He certainly has a solid acting pedigree (40 citations on the same), and kudos for an appearance in Fox TV's stellar The X-Files during its run. Hailing all the way from his birth in Joliet (IL) of all places (not all that far from where I was born), Rapp keeps his head on the ground but reaching for the stars ... and now he'll get some!
But I've been a huge fan of Doug Jones (picture above left) for a few years now. Folks don't often recognize the talented actor as his most prominent work tends to be under heavy, heavy make-up: he was Abe Sapien in the Hellboy franchise, and most recently he played one of The Ancients aboard FX's The Strain. He'll joined Discovery as Lt. Saru, and despite my disdain for the property going the way of 'the stream' I'll be interested to watch his work.
As always, thanks for reading ... and live long and prosper!