If 15" is much better than 13", is 17" much better than 15"?
Here's what you basically need to know.
1. Whether it's a 13", 15", or 17" MacBook/MacBook Pro...you can always attach an external monitor when you are at home for extra screen real estate.
2. You need to decide how much laptop "foot print" and weight you want to haul around when deciding between a 13, 15, or 17" MacBook/MacBook Pro.
3. Only the 15" and 17" Apple laptops have dedicated graphics hardware (better graphics hardware). The 13" has "integrated" (slower) graphics hardware.
4. Basically the only upgrades you can do on any of these laptops is ram & storage space (which is something you can be concerned about after the purchase).
When you do decide on a specific model Apple laptop to purchase...you should verify it's max. ram...just so you know your future ram upgrade options.
HTH,
- Nick