I'd agree with the other sentiments here. Advantage of the Stick is it works a little better out in a windy paddock, otherwise MIG all the way. Certainly can't beat the MIG on a bit of RHS work. MIG seems to need some more balls. I've got a 150Amp WIA running CO2 (because Argon is a lot pricier), it works fine on 3mm stuff. 6mm it would do, but you'd have the dials wound up pretty well and at least in suburbia, depends a bit on what time of the day it is. Some newer houses are using some pretty light wiring, even when running 15A to the shed. It'll handle it alright, you just get a bit more voltage drop and it doesn't seem to perform quite as well as it should. Though that could just be MIG's as well, my Brother (professional welder) calls them the 'females' of welding machines.
I'd look at consumables as well, more the availability than the price. I had a nice Bernard handpiece on my machine, but was starting to have issues (age and neglect) so ended up with a Tweco (I think) handpiece which while not as nice, was a lot cheaper and will cope with the handyman type use I'm exposing it to, as opposed to the Industrial use that Bernards and what have you are designed for.
Seen a few people with the SIP machines, another cheap welder with limited controls, but haven't heard too many people complain about them and from what I've seen, half the price of the WIA equivalent.