start with the 30amp and that will probably be all you need. BUT if you can leave room for expansion through your cash at things like more space for circuit breakers OR ifind out what it would take to get 3phase IF it's even possible. If your like me your always wanting to try things out and your really limited by what the person did before you. Also if you can think about what things your going to have on at the same time plan for that... for example a compressor that pulls 10amps on start up and then drops to 8 amps for continued use is perfect for your circuit, but if your running a plasma cutter that draws 15 amps and you have a shop air quality fan that draws 5amps. The second that air compressor kicks on, and it will because your running a plasma cutter, boom your going to spike overload in the middle of that beautiful cut you were doing.
but 30amp 220v is totally enough for thousands of fun things like welders, plasma cutters, milling machines, lathes, lazer cutters etc.
Also as a side note, I'm pretty confident 30amp 220v is plenty for things like Variable frequency Drives, and Rotary Phase Converters if you're ever shopping use 3 phase equipment so really as long as you have space in your breaker box and are willing to run the lines it's almost better not to prerun anything and just add it as you get equipment. So I'm basically agreeing with Bud16415. Then your only spending the money on the things you use. I'm constantly down the rabbit hole of adding things because I found some deal on craigslist or the like.