ARC or MIG will do for what you're wanting to do.

Main points to consider are -
MIG will be quicker/cleaner but you have the additional cost of sheliding gas (and the associated rental).
A good inverter will be far more versatile, as it will give you TIG capabilities, which is very handy if you ever do thin metal work.

I've got a Clarke 255TE MIG, which does the majority of welding, including anything from 0.8mm sheet upto 1/2" plate.
I've also got a Cebora inverter (ebay bargain!), which is ideal for heavy jobs where it's just not practical to haul the big welder to (plus there is the issue the MIG needs a 32A power supply), but also gives TIG capability for anything involving thin metal.