I do not feel comfortable with Brad Smith as a #2. The guy just got here and he is playing multiple positions. Give him a year and then maybe. Thigpen also just got here and hasn't got a good feel for his receivers. I'd give him a year too.
Brown has done some improving though not as much as hoped. For now, I think Brown should be considered for the #2 spot.
Smith will get some spot duty at QB and WR. He will also be used as a decoy occasionally, IMO.
So far, I am just not impressed with Thigpen, but I do think he needs some more time to adapt here.
Overall, I am not overly worried about our QBs. I think they all will bring something to the table with time and practice. My biggest concern is seeing better performance from the linemen protecting them. It's not looking good for Hangartner or Wang. Both look pretty weak this year.