Hands down, the TIG process is better - no two ways about it. No sparks, very little warpage and you can control post flow along with every aspect of the process.
However, it takes about three times the prep work and three times longer to do the weld. Your filament with TIG needs to be tighter and cleaner. The patch panels are much more labor intensive to make and fit. Everything, including your gloves needs to be clean. Better, but hard as heck and very time consuming. You even to have a dedicated grinder to sharpen the tungsten electrodes or it will pick up contamination. TIG is the brain surgery of welding.
AND, like others have said - requires a lot more skill - like tons more skill. However, if by chance you have proficiency in gas welding with an oxy-fuel torch (oxy-acetaline) then you will pick up TIG in a day. Gas welding is the hardest of all to master - especially on sheet metal.
With a good teacher and a quality welder, you can learn to MIG weld in a short time.
i'd recommend that you do not try to run a bead when doing rust repair. Just fill in the weldment with a series of spot welds. For that reason, I'd recommend that you buy a Lincoln Power Mig with the optional spot timer module or the Esab Mig Master that comes with that option standard. You can dial in the machine to get just the right size spot each time you pull the trigger. Easy Peasy.
I love the TIG process but wind up using MIG for nearly everything. Tig is great for welding inside a nice car where you don't want to damage stuff with sparks.
Check out Ron Fournier's DVD's on metal working.
He is so good that bondo is referred to Fournier in a can because he uses no body filler.