From what have been written on this forum before, the smoothest one is probably the Husky 350, closely followed by the 353.
2150 and 2152 are Jonsereds versions of these saws.
All these are probably at their smoothest and fastest with NK bar and 95VP/H30/S30 chain.
I think all saws in the 3 cube class are at their best with 15-16" bars.
20" should be OK for occasional use, but cutting speed will suffer.
353 and 2152 are pro quality saws, 350 and 2150 are "farmer" (or top of the line "homeowner"-) saws with a bit less power and plastic crank cases.
If you want more power I suspect that Husky/Jred still are the smoothest, but the MS361 is reputedly much better than other Stihls. I have never touched 357/359/2156/2159, so I don't know if they are smoother than the 361 or not.
I have no complaints about the anti-wibe on my 361, but must admit that the 353 is noticeably smoother.