I prefer 035 wire, it welds hotter on the same setting as 030. for welding sheet metal I go clear down to .025 then turn the machine up, it works better for me for penetration.
I like the 35 better too on every machine I have ever used except for my Miller 210. On the 210 .030 runs so much better I can see no reason to ever run 035. It also puts spray transfer with the C5 gas I get more into reach of the machine (it is still at the top end and I would not like to run it for extended periods)