All of my shirts are either slim, or extra slim fit. What I find (all my shirts are Charles Tyhwrit) is that they just tend to hug the shoulder better and are more tapered at the waist so when they are tucked in, you aren't left with the baggy overlay that an oversized shirt, or a regular shirt from many brands can give you. I'd recommend going with slim fit for anyone with even a body shop slightly larger than average. Go with regular only if you really struggle for room in your clothes. I just prefer how they fit. My definition of slim-fit is not that of the euro skinny fit either. That's the whole topman thing. I can't stand that.