It depends on what you're after. I work with fine silver, and I had
the opportunity to try an arc-welder at Rio Grande's Catalog In
Motion in Tucson. I found that the joint was secure, but it looked
"splattered", to me. I do butted joints and then solder them closed;
I do a lot of them, and it's a point of pride with me that most
folks can't find the joints. With the arc-welded one it was very easy
to see, and after I got home I repaired it with a torch, to flow the
splattered parts back into the body of the joint.
I don't know for sure if a spot-welder would do the same thing, but I
suspect that it would. I'd use spot-welding and arc-welding (and
laser, which I found unsatisfactory with bright silver) as interim
measures to hold something in place until I have time to come in and
perfect the joint with a torch. That's just me, no doubt.