Line choice can depend on a few things, such as the size of flies you plan on fishing, their weight, and how heavy will the sink tips you will be using. Polyleaders/versaleaders or T-material?
Skagit is a great way to get started with spey casting since the head is short and heavy and is great for big heavy flies and heavy sink tips.
Scandi line are a bit longer in head length and can cast moderate to large flies as well as handle various sinktips. Just not as heavy that the skagit can handle.
I started with a mid belly line which isn't great for big, heavy flies and heavy sink tips, but I don't fish alot of big stuff or heavily weighted flies and I prefer to use poly leaders. I chose to start with a midbelly line because if I can learn to cast a head that is 50-60ft long than scaling back to a skagit or scandi would be no trouble.
Airflo Delta spey is a great line to start out with if you choose to go the mid belly route.