I feel with "pet holes" these glimpses make them even more spectacular - especially C. fimbriatus, I own C. dyscolus, though still a sling it looks stunning they also have superb appetites and a fantastic feeding response - so that's a vote for C. fimbriatus.
I agree on the C dyscolus. I have just a brown one (no special color morph). The feeding response is so good, I routinely see her. Not that she hangs out on top, but she goes right after the roaches and heads back down the hole.
Mines is the "Vietnam blue" I believe, well that's what it was sold as, it does have some blue colouration to it, which will in time become more prominent as it ages - it molted last, last evening, I'll post pics once it's hardened and has had a meal or two....
Paid fifteen dollars for my dyscolus blue as an unsexed sling. The electric blue go for about ten times more. Ludicrous for essentially the same spider, looks and behavior wise anyway.
The blue definitely darkens as they grow, becomes more apparent with each molt.
. Electric blue is a litle bit overrated imo. 
That's how I house my smaller fossorials as well! Visibility is never a problem
Mines is probably a molt away from being that size, as said a beautiful spider, thanks for sharing....
Prefer looks over size. Same reason I like T Stirmi over T Blondi. Even though blondi gets bigger its uglier.Fimbriatus is best looking, thats for sure, but it is tiny. Don't you want huge beast like huahini or kaeng krachan?
It doesn't get any bigger. In fact, most of the largest Theraphosa reported have been stirmi.
Is 4 inches enough? I'm asking because if not I have to make a taller enclosure.
I love to offer to (adult) burrowers always, at least, a good 8/9 inches. When it comes to H.gigas or the like of P.muticus, 12/15 inches.