My favorite MK resort vs my favorite Epcot area resort. A split stay is not a terrible idea if works with your park passes (Epcot and HS while at BW and MK at CR - I'd even Uber to AK from CR even though it's a little bit further, just to spend more time at CR)....maybe too complicated if this is your first trip.
All and all, it's really quite equal IMO b/c -
-BW gets you walking distance to two parks and CR one - but MK is the most important to be closest to b/c you cant park or uber there (plus you can monorail to Epcot via TTC).
-BW has the dining on the boardwalk and Epcot, but Contempory has its own including the new Steakhouse 71 and just a monorail ride to Poly and GF.
-BW has a better pool slide, but the CR pool overlooks Bay Lake, which is a better atmosphere and a nice escape. For an 8 yo, the CR slide will be plenty exciting enough.
-BW is more fun/lively at night on the Boardwalk, but CR has the water pageant and your 8 yo will probably be ready for bed. A monorail ride to the Poly for an evening Dole Whip is always fun as well.
The Garden Wing is not quite the same experience/convenience as staying in the tower, but I'm not crazy about the incredi-rooms, so I don't think it's a bad choice at all. You really can't go wrong with either hotel, but with an 8 yo, I'd probably lean CR and definitely pay for park hopper so you can go to MK at your convenience later in the day/at night. If you are paying to stay that close, you don't get full value w/o park hopper. I'm not a huge fan of the bus rides, so I would Uber it to HS and AK. Small money in the context of your whole trip for much faster travels. Good Luck!