I have mig, tig, stick and oxy acetylene, it depends on what you're welding.
When I built my trailer I used stick because per foot of weld, welding rod is dirt cheap compared to mig because shielding gas prices keep going up.
But for most motorcycle frame welding, and the majority of projects welding mild steel, mig is good.
I use a Millermatic 255 with 035 wire and the additional spool gun for aluminum. Its a fantastic welder but priced out of range for most hobbyists or weekend mechanics. I also have a smaller Hobart 145 with 023 wire that I use for thin sheet metal as the heat range is much lower than the miller. I dont think Id weld a frame with it though.
Come to find out when I was talking to my dad today I found out in a bunch of tools we got from my grandpa when he passed away years ago was an oxy acetylene setup so I'm gonna start practicing on that with just scrap pieces of metal to get use to the flow moving molten puddles.
I do have experience with OA but only brazing copper and brass
Mig, tig, stick, no Oxy Acetylene.
That's for fixing broken exhaust with a coat hanger or real brazing..... not structural repairs.
Harbor freight mug gun with coupon, get flux core, will do what you need and be cheap.
No Sig, someone whined and I lost it.. Crybaby....
Flux core has less spatter than mig but runs hotter. I was a welder for 15 years. Tig is a stronger weld, but tends to be more costly. Keep in mind if you're welding, that it isn't just the weld but also the fit up. You want to make sure you weld to good metal and remove any paint from the heat affected area. If you notice porosity in your weld, you need to grind it out and re-weld it.
Welder? Um.... How about a 1963 Sears/Craftsman Arc Welder? -- it was my dad's from way back in the day. I have all his stuff, his welding shield, countless boxes of various welding rods, but no owners manual at all. My dad is no longer here (RIP, Pop... 1922 - 2002, 80 yrs old at his passing), and I've messed around with the old Arc Welder from time to time, and have no clue what I'm doing.
All I know is it is wickedly powerful, and I have to unplug the dryer from the outlet in the laundry room, plug in the gigantic 240v extension cord, then out the backdoor, and then plug the welder in from my back porch stoop. I've toyed with various plug-ins and amps and whatnot, and I was at least able to create a big burn mark down a scrap piece of metal (clamp/negative charge one one side - and the welding rod/stick (positive) ever so lightly touching the scrap metal, to where it made a massive spark, and a big strip of molten metal about 3" long.
How do you weld something with an old 1963 Arc Welder? I have no idea...