We've had some wonderful trips with our twins since they were 7 months old until now at age 4, listed below in my sig. We've always stayed deluxe mainly for the ease of getting to and from parks. If your main park will be MK, then yes it is great to stay at a monorail resort. We enjoy Poly and CR, have never stayed at GF. I wouldn't go by other people's experiences, really, because everyone has a different experience, some good and some bad all at the same resort.
WL is also a great resort that is only a boat ride away from MK, so it's easy enough to hop back to the resort for a midday break. At least I hope that's the case because we're staying there next month!
If you think you'll frequent Epcot and the Studios a lot, then BC is a great resort for your child. It has an awesome sandy-bottom pool area that makes for hours of fun for the little ones. It is the ONLY pool in Disney where I can actually relax on a chair while my kids play for hours right near me.