Based on pre season game 1 edge goes to Stewart. But I think Bunting can rebound and push Stewart. I think it may come down to a pre season game 4 decision.
https://www.buccaneers.com/news/m-j-stewart-brings-toughness-versatility-to-nickel-battle
My gut feeling is this: I was surprised to see the coaches playing Stewart so much out there all over the field in pre seaosn game 1. My initial reaction is they are trying to gauge what progress he has made from last year to this year. And also see if he has shored up weaknesses in his game or what his limitation are still self evident. The other reason is that Dean is injured and R. Smith is out the first four games. R. Smith is clearly the #3 CB on the squad currently and when he returns during the season. However, Dean could close the gap if he comes back quickly and competes.
What I noticed is that Stewart is playing better technique and is actually not lost with what is going on. His footwork is still suspect as he has a tendency of tripping up but it is improved compared to last year. Stewart is turning his head around now to look for the football.
As SR has noted he is still often in at trail position but I am not privy to what DB coach Ross and the coaching staff are expecting out of Stewart based on his build and metrics.
For Dean Murphy-Bunting he just needs to play more aggressively and do his assignments like in OTA sessions. To me I think he just needs to play smarter and faster which I anticipate will happen in pre season game 2 IMO.
Currently Stewart is the better box players while Murphy-Bunting has the upside to be a cover blanket for any slot WR due to his size/speed combo.
May the best man win.
P.S. I am a huge USF Bulls fan and I would love to see Wilkins given a shot at the nickel CB job.