Which ever kind you'll wear. Just like sewing your own clothes, knitting your own garments means you have much more control of what type of wool you use for each project.

Jumping in here as someone who grew up on a specialist sheep wool farm, I would highly recommend commissioning a knitter to make you a sweater in a style you like, to your measurements, from Wensleydale wool--its a rare UK breed and has wonderful, slightly shiny, durable long staple fibre. Soft enough to wear against my sensitive skin. Not cheap, but definitely (esp if you hand wash carefully and flat dry, and learn to darn) a BIFL option.

I'd avoid your typical Aran shop--the tourist and international trade means, as said above, that they don't often use legit local wool and it's often lower quality and itchy.