Wow, you are lucky to be able to plan your house!
Best of luck with it.
I have a formal living room, and a big dining room. I never use them, since my family is small; only use the dining room when my parents and my brother and sister come with their spouses. I DO have a huge eat in kitchen, which adjoins the rec room, all open across the back of the house. THat is nice because when people come they end up either in the kitchen or the rec room and everyone can hear and see each other, no matter where they are.
My Two car garage is great. Walk in closets in master bedroom. Large master bath and 1.5 other baths. Whirlpool tub is nice for when I DO use it for myself (about 4 times a year) but I give my kid a bath in there every night so it does get used. Bedrooms that are at least 12x12. A partially finished attic gives me additional storage (no basement).
Things I'd have liked to have: A stairway at the back of the house, not jumping out at you the minute you walk in the door (unless you will have room to plan a grander staircase within a foyer). Basement is something I miss, so is a mudroom. Oh, and I prefer 10ft ceilings instead of 8ft. I always would have liked to have the rooms divided by pillars instead of solid walls, gives the house a more flowy feeling and lets in more light and air movement.
A front porch is indespensible to me, as is a sunny kitchen, IF the house is facing the right way. Will you have a choice as to how your house will sit on the lot? To me, that is important - feng shui and all that - I love a sunny kitchen and rec room. The front of my house faces north west and the back where the kitchen, rec room, office, kid bedroom and other guest bedroom are faces southeast - lots of sunshine in the kitchen and the front porch is shady when afternoon comes.