If your sfter a middle of the range, as mentioned Clarke are good for a budget. you want around the 130 amp mark, go gasless, you can change it to gas and use both. Gasless is good for outside as the wind can blow the gas and not shroud the welds! You have to use the flux impregnated wire with the gasless. Gas is as mentioned great for indoors, but you have the extra outlay on the disposable cylinders. Get friendly with your local Pub
, their co2 bottles are cheaper and last a hell of a lot longer.
If you go down the route of buying the correct gas bottles, get a co2/argon mix, gives a much better weld.
If welding stainless steel or aluminium you need the appropriate wire and gas to suit.
Ive been welding since i was 10, im 45 now and my first mig was a Clarke 100 gasless, lasted me for years.