Different welding jobs require different welding processes. If you think you might work with all three main types of welding process, then a multi process welder is definitely worth the money. It will save you money as you get one machine to do three processes instead of three separate machines for three processes. They also use up much less space in your workshop, which is important if you only have a small workspace or want a portable all-round unit.
All the multi process welders listed can perform MIG, TIG and Stick.