Hello, Imen!
Great question! Each level of resort at Walt Disney World has its own magic, benefits and charm; you won't be disappointed if you choose wisely.
Value Resorts obviously will provide you the best "value," so check out
Accommodations at Walt Disney World Resort to compare options. Disney's All-Star Music as well as the brand-new Art of Animation Resort also have
Family Suites, which sleep six, include two bathrooms (!) and a mini-kitchen.
For Moderate Resorts at WDW, consider The Cabins at Disney's Fort Wilderness Resort, Disney's Coronado Springs Resort and Disney's Port Orleans Resort-Riverside, each of which include rooms or suites that sleep 5 or 6. Resorts in this category also have slides at their main pools. (Great for hours spent poolside!) While the Cabins at Disney's Fort Wilderness Resort are pricier than some others in this category, they come with FULL KITCHENS, making preparing a meal or two each day in-cabin a breeze, and a real money-saver, too. Pack a few bags of breakfast, lunch and dinner non-perishables and you're good to go. Refrigerated items are available at the resort store, or at a grocery store on drive into the resort.
Regarding resort transportation, I feel it's more convenient to rely on resort buses, boats and monorails. I like being dropped off at the parks' "front door," so we get into the magic that much more quickly, and with less hassle.
Please send more questions as you narrow down your choices for your birthday celebration vacation! I'd love to help!