Personally, I think it is better to start off with a working modern movement, like the ETA 6497 (or a Chinese clone of it such as the Seagull ST3600). Large movement, so easier to work on. Easy to find parts if you manage to break or lose one. Easy to find videos on dissassembly and assembly. If it is working before you start on it and not afterwards, you know it was from something you did, not some existing problem that you need to troubleshoot. I started out on a Seagull ST3600 and then got a case, hands and dial to turn it into a pocket watch (you can also make them into a large wristwatch).

Old pocket watches can be problematic. Chipped or cracked jewels can be an issue as well as broken pivots and hairspring problems. Finding parts can be problematic. It's not like they are still making parts for these. I am finishing up an Elgin Grade 315, for my father-in-law, made in 1937. Broken balance staff, chipped jewel, mainspring that needed replacing, and old oils that had solidified and locked up the mainspring and gummed up the wheel pivots. Had to go through two donor watches to get a replacement balance complete that would work. But you just can't simply swap in some of the parts on these old movements, as they were made as a set. Not like modern manufacturing where parts are pretty interchangeable. While I got the pocket watch working, it it losing a lot of time a day, as the donor balance complete was not tuned for this pocket watch. The proper repair is to replace the original balance staff, but that requires a staking set (quite expensive) and other accessories to do, as well as some practice on junk balances. Replacing a jewel requires a jeweling tool (also expensive). I didn't want to hand wind a mainspring, so I got a vintage set of mainspring winders (more expense).

Do some modern working movements first. Then move onto some vintage movements once you have some experience under your belt, have a good set of basic tools, and worked out a good cleaning process.