It depends on what you wish to use it for. For SD/HD I'd probably tell you to get the Glock. However, this is not to say that a Witness pistol is unreliable or failure prone.
For general range and recreational use, either will work, it will come down to personal preference.
Warning: The Witness pistol is usually a quality piece. However, they are a bit of an act of faith. EAA, the importer, has developed a reputation for poor/hostile customer service. (I haven't had any dealings with them, so it's hearsay on my part) So if it was your only SD/HD firearm, it could be a problem if you're waiting for them to get around to doing their job. As I understand things, Glock's CS, while not always stunningly wonderful, is usually pretty good. So the odds of having a satisfactory CS experience is better with Glock. http://eaacorp.com/
Greg USAF Retired NRA Life Member "If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." Milton Friedman
Yea , I mean you're right there 5'11 174 isnt small . I think you could handle a 20 no problem. You're a bit smaller than I but not by much. Make no mistake the G29 is no pocket gun and the G20 even more so. You know your carrying it. But I use a universal leather holster you can check out on my youtube channel 36gh0zt36 if you wanna see how I carry it and I mean you know its there but I have NO trouble concealing it with that holster and it's fairly comfortable doesn't bother me really .
When driving it's a bit more noticeable since carrying at 1 O'clock its articulating into your stomach but again its not unbearable. I don't think I'd want to take a 150 mile drive carrying it like that but 30 min drive is no worries. And the thing I like best appendix carrying at 1 O'clock is the more you bend over the more concealed it is. which in your case coulda helped
And I dont own a g29 but I could only assume seeing the G20 is easy enough to carry the 29 would be nooo problem at all.
Again hope this helps. I love my 10mm it's an excellent defensive round with enough power to handle any BG