Mig is the way to go for a hobbyist who won't be using the machine on a regular basis. Easy to pick up and make great welds, easy to adjust- especially if you get one of the Millermatic units, and will last forever.
Tig machines make great welds, but you need to stay in practice and learn how to not only use your machine, but to set it up and maintain it, sharpen electrodes, etc....
99% of the time, the Mig welds will be more than presentable for the work you will be doing and there is no real set up time. A couple practice passes on some scrap metal and you're on to your project.
I have a 110V Miller 135 Mig and used it exclusively for my scratch built cobra welding and it worked great. At times I pushed it to the limit but it never gave me a bit of trouble and the welding came out great. A few of my other projects needed more power, so I looked around and bought a used Millermatic 251 machine that will handle anything I can throw at it for my lifetime. I would love to learn to Tig, but just don't have the time to take it on right now and not enough projects that require Tig to make the investment worthwhile. If that changes, I'll be shopping for a Tig and a good Tig welding class.
Remember that any of these machines will require some accessories on top of the initial price. A spool gun if you want to do aluminum will run anywhere from $400 to $750, depending on what you will need and the size of your machine. Also, a good 120 CF bottle of shielding gas. I found a bottle on craigslist for a great price as my little 40 CF bottle always seemed to run out at just the wrong time.
Here is one of the better prices on a machine that would probably be perfect for you if you aren't into structural work-
Miller® Millermatic® 180 Auto-Set
Bob