Tig is nice but only if you want to weld materials that have heat considerations like Stainless, Ti, Ali etc or thin materials. Also To weld Ali and other exotics requires much more expensive gases like Pure Argon or Argon & helium mix etc so unless you have need for cosmetic welds and thin heat sensitive materials then for the run of mill steels then much quicker and cheaper with MIG.

Then you have the learning curve which is much higher than MIG or MMA esp when you talking Ali etc. You'll use much more consumables with TIG when learning because just the slightest touch down of the tip means stopping and redressing the tungston otherwise your always going to struggle.

Also Don't buy a Cheap Tig if you plan on welding Ali or more exotic material or thin material and cosmetic welds etc because you need the flexabilty of the settings and they are often limited.

For 5mm steel I'd go MMA for the cheapest option or Big Mig with decent duty cycle.