Heads and sink tips are basically fancy "leadcore" in pre-determine weights and lengths. You just swap em' out as needed over your running line.

It's easy to make cheap bulk heads from LC. That's how we did it long ago before Jim Teeny started his thing and they became commercially available. All you need to buy are the replaceable nylon loop-to-loop connectors for each end. A nail knot would work, but you'll want to be able to change out heads as conditions call for it, so speed loops are the way to go. The only knot I ever tie is directly to my fly.

You can use a W/F sink tip and add small heads if you want. But if you only had one line to buy, buy a do-it-all WF floating line and add bigger heads. It also depends on how you want to fish. Swinging flies, stripping flies or nymphing? But that starts to complicate things a bit for several reasons. Spokey wants to strip flies, so that's the context I am going with.

As an extreme example, I've fished most of the Rio T class lines Stonefish is referring to above for DEEP pool nymphing. Key word nymphing, not stripping. Heavy, heavy tips. 16 - 20" in / sec sink rate class heads. You can pretty much go as deep as you want with proper rod and line handling skills (and current). 6' deep is nothing really. I'm talking 20 - 25 foot deep slow pools where I hear some big browns or a King or two might live . But those heavy lines are exhausting after a full day of fishing, not just from casting, but from mending, highsticking and Leisenring lifting all damn day. Plus you gotta be right over the fish (the inverse of Spey fishing) and the fly may only be in the zone fishing for 1 - 2 seconds. It's a lot of work.

One of my favorite fishing moments in Washington was going up to Reiter on a busy winterrun day and busting out my Scotty 5wt loaded up with a heavy Rio depth charge to a size 12-2xl bright red stonefly nymph (a trout pattern that I re-tied into steely colors). The crowd snickered until I promptly nymphed up a nice 5-6 pound hen on like my 5th cast. The look on their faces was priceless. Like...what just happened and how?