I would highly recommend using ME. It is great, especially when traveling with kids. I couldn't imagine having to try and recover my luggage at MCO, and get my family on a bus or to the rental car counter. They do specifically state that it could take up to 3 hours for your luggage to arrive. Be sure to pack any necessities in your carry on (like bathing suits). We got on the bus with no problem,checked in at POP, went to the pool, and when we came back......LUGGAGE! It is magical, and was pretty fast too!
What you also need to remember is, that some days (Saturday and Sunday especially) there are often 10-12,000 people checking in to a WDW resort who use ME. It is an incredible feat for them to process all those bags and move all those people.....and don't forget the people checking out too! We arrived on a Monday, and our bus driver said there was only about 5,000 people coming in on that day.