There are people a lot more "in the know" than me on welding. I have always used a stick welder on fence corners. Something about penetration of the weld, ease of use. I don't know all the ins and outs. But I do know this, I see guys out building pipe fences and don't think I have ever seen one of them using a wire welder. They may own one, but it stays at the shop most of the time. I asked a couple of them and was told it had to do w/ wind blowing the shielding gas away from the arc. Wire welders it seems work better in the controlled environs of the shop. May be a cost thing too, but I don't know what consumables cost for wire since I don't own one.
As far as bolting corners together for takedown, hmmmmm.... I remember few times we ever needed to move a fence, but that is us, your situation may be different. When we did move a fence corner/brace, it involved a torch and a tractor w/ a loader.
Biggest reason I bought a welder (Lincoln ranger 10) was that at $35/hr to hire it done, I could pay for a welder w/ savings. I am no master welder, but stuff I have stuck together has held so far. [img]/forums/images/icons/wink.gif[/img]
Also, I have found lots of projects around the ranch that are a lot easier when you involve a welder.