The bag issue is the one main reason we won't use Magical Express.
I've heard horror stories about the delays of luggage delivery, from an hour or so to most of the day. That's great if you're arriving first thing in the morning and have all the time in the world - we don't.
We are on the later flight from Gatwick, which means we don't get there till that little bit later. But the time we get to the hotel and check-in we have been up for virtually 24hours with no sleep (i'm usually the only one that can grab a few hours on the plane). Therefore, we literally unpack the moment we get to our room, then fall into bed, so we're ready to go first thing in the morning, and already adjusted to EST!
Any delays in getting our luggage, whether it be an hour or 6 is too long for us. So, we just go via the normal transfers. We've never had a problem with them, and we don't really care how long it takes because it's not like we're going to go to a park after we've checked in, so it's no skin off our noses!

But of course, that's just us!