TIG or MIG welder

[m_c]

MIG is far easier to learn, especially for steel. It's also one of the quickest welding methods, and if you use gas, requires little post weld cleanup. It will also tolerate slight contamination (i.e. rust/scale), unlike TIG which will errupt at the slightest sign of contamination.

TIG is one of the harder welding methods to learn. Best way to think of it is essentialy gas welding, but with an arc, however due to the sheilding gas it allows a far wider range of materials to be welded. It is an inherently slow welding method, and is far more suited where MIG or Arc can't be used. It's also more expensive for the required gas. Last time I priced it, pure argon was nearly twice the price of argon/co2 mix used for MIG welding.

Alot of TIG boxes are also capable of Arc welding, and are far easier to use for Arc due to the well regulated DC source (the cheap buzz boxes can be a right PITA to get going). However Arc takes a bit more practise than MIG, as the flux hides what's actually happening at the weld point, so you have to rely more on knowing how fast you should be moving so you lay down enough metal, rather than eith a MIG where you can see how much metal you've put down.
The same comments also apply to gasless MIG, as it's essentially Arc welding but with a continuous feeding rod.

My first preference is always MIG.
Arc gets used where either I have to run of a 13A socket, I need to use Low Hydrogen rods (the saviour of repairing carbon steel!), or I'm welding something where more heat/penetration is needed.
TIG is usually used when I want to play, or on the occasion I need to deal with Stainless.

[EddyCurrent]

I need to use Low Hydrogen rods (the saviour of repairing carbon steel!),

I used to work with a load of welders and this is true, they always went for low hydrogen rather than mild steel rods.