[Karibou]

It really depends on what situation each connection is going to be in.

I'm a huge fan of bolting whenever possible, especially if there's a chance that the metal in question is going to be unconnected or changed at any time. As long as you can easily reach both nut and bolt (unless you're ambitious and tap EVERYTHING), fasteners are great and reliable ways to keep those metal pieces snugly together.

While rivets are great for sheet metal and all, don't use them in high-stress or high-impact places...they can pop out (speaking from experience). They're easy enough to drill out if necessary, but I would hope that you don't use them with the intent of drilling them out every so often to upgrade or change parts. IMO, they're great for sheet metal (if used right -I'm not a fan of sheet metal after my experience with it this year), and fantastic for wheels.

Welding is a great option for parts that can't be riveted, and their structure is such that you can't easily bolt it together. As long as you don't intend to take apart those two little pieces of metal ever again.