To add a few things to George's excellent answer:
I would simply place the sub-panel in the shop
This is a key. Because the garage is attached, you can run each circuit as a home run back to the subpanel-next-to-main-panel. But putting the subpanel in the garage has some real advantages:
- Feeder from main panel to subpanel can be aluminum. Large size aluminum wires for a feeder will almost certainly be less expensive than several small size copper wires for individual circuits.
- Any time you have breaker trips and any time you want to work on add or change circuits it will be much more convenient with the subpanel in the garage than in the main house.
If you actually want a subpanel next to the main panel because you need more circuits for the rest of the house, add two subpanels - one in the house and one in the garage. Panels are actually pretty cheap - you can get a 20 space (that's spaces, not "circuits") for $100 or less.
Also keep in mind that the wire size has to match the feed breaker. You could have a 42 space subpanel with a 200A breaker if you get a good deal on one. But if you only need 90A (which happens to fit with some good aluminum wire prices) and you use a 90A breaker in the main panel then you don't need to use expensive 200A-capable feeder.
Most importantly, for any circuit (feeder or branch), pick either cable or conduit with individual wires. Never use cable with conduit - it costs more (you're paying for the cable sheath and for the conduit) and running cable through conduit requires larger conduit than the equivalent individual wires require.