Haven't used the Miller and I'm not an experienced welder but I've been researching a bigger machine to replace my little Lincoln SP135+. After a lot of reading and spec comparison I ended up ordering a HTP MIG 200. It should be delivered this week, so I'll be able to give better input as to build quality and performance shortly. At half the price of the Miller and WeldUSA's service reputation it was hard to argue.
http://www.usaweld.com/SearchResults.asp?Cat=20
I also ordered their 221 Invertig and 600 plasma cutter. A friend has the 221 TIG and is very pleased after a few months of light usage. So it's not a total gamble.