I think the Studios is better to do first. Everyone gets there, sees the big coasters and says wow, I want to ride that, and heads into Islands. Also, everyone will know that the Studios will be open later so they should go to Islands first. That means there will be more people at Islands. If you go against the grain I think you'll probably have better luck.
But I wouldn't even worry about it, the crowds won't be too big until the holidays. Don't get me wrong there will be a hefty amount of people inside the parks, but compared to peak times, it really isn't that bad. no than 5 - 10 minutes for anything. Most people spend so much time walking around trying to figure out what to do that the actual lines aren't that crowded. If you have somewhat of a plan, know what you want to see, you'll be able to hit all of those things plus things that you weren't expecting to be able to do. And don't be afraid to deviate from "The Plan", for instance you may cancel dinner at Epcot's France to get dinner at Italy. We made several last minute reservations, and several walk-ins, and had success. They like to scare you by telling you everything is "all booked", but when you consider that WDW does not reserve or hold tables, that doesn't mean so much. We had ADR's at Cinderella's Castle for dinner and still waited 45 minutes, but waited less than 5 minutes at the Coral Reef at Epcot without reservations. It all works out with a mix of planning and sponteneity. Just don't be like the guy we saw in the Italy pavilion who made an *** of himself yelling at the hostess that he had booked a table and it wasn't ready. People get very angry when things don't work out just the way they planned it, but you can't let it get to you. Italy was too crowded that night so instead we walked back around to the Land, watched Soarin again and had dinner in the cafeteria there - some great chinese food and the freshest chicken ceasar salad.
Also, having ADR's for every night can get EXPENSIVE. By the third night you'll be longing for a $9 cheesburger and a $3 soda. Plus, if you eat a couple of smaller, cheaper meals at Epcot, you can share a slice of cheesecake in France, get some gelato in Italy. Sorry I'm rambling, i just like thinking about the whole trip, it was so much fun.
