Bellagio:
Pros
A true 5 star property.
Great high end restaurants - Le Cirque, Olives, Picasso, Prime
Great shopping (high end - Tiffany, YSL, etc.)
Great free stuff - conservatory, fountain show
Beautiful property
Cons
Pricey rooms & restaurants - a hot dog is $9 in the snack bar at the sports book; and the dinner buffet is about $37 per person. Room rates bottom out at about $169.
Only one show - O by Cirque du Soleil; best tickets are $165 per person
If your room is in the main tower, you have to walk through the casino to get to your room
If your room is in the spa tower, you have to walk down a long hallway to get to your room.
If you rent a car, bring your patience. There is only one entrance & exit for automobiles; and it's on the Strip.
Venetian:
Pros
Great restaurants, especially for celebrity chefs (Emeril, Wolfgang Puck, etc.)
Great shows (Blue Man Group, Phantom, Jersey Boys)
More variety of shopping (Grand Canal Shops)
Easier to enter & exit property by car; has 2 entrances, on on Strip & one on Koval at the rear of the property
Spa is REALLY nice - Canyon Ranch Spa
Cons
Property is HUGE. You will walk a lot, EVERYWHERE on property.
Everything is pricey. Gondola rides are about $15 per person. Admission to Wax Museum is about $25. Room rates bottom out at about $199.
Don't know if it's important or not . . . Venetian is non-union property.
If I had a choice, I'd stay at Bellagio.