Both the trek in and out were different between the two companies. 

Trekking into Everest base camp
With IMG we camped nearby the grounds of lodges on our trek into BC, with the cook staff preparing our dinner in small sheds.  Usually we were able to eat inside the lodges, although sometimes a dining tent was erected.  I am really not sure why we did it this way???  The lodges were empty as we were ahead of the peak trekking season.  I can tell you that when you are about to spend the next 2 months in a tent, the thought of camping right beside a nice lodge is not appealing.  There is an argument that having our cooking staff prepare the food, instead of the lodges might be safer, but several people still got stomach upsets, including me.  Perhaps it was food we might have eaten elsewhere?  This year, despite only eating at the lodges, I didn’t get sick at all.  I think that staying at the lodges is definitely more comfortable and preferable to camping, and is why all the $50-$70K expensive expeditions do it.

Trek out from Everest base camp
On the trek out this year, Asian Trekking sent a staff member out with us and that person paid for the food and lodge accommodation.  We did have a mix up with our bags and that meant that the bag that was meant to come down with us to Lukla was sent by express porter to Lukla, and one of the expedition bags was carried with us instead!  However, it was no big deal.

In 2006, IMG gave us an allowance and we had to make our own way unaccompanied back to Lukla.  We didn't have porter support on the trek out either, although this is more of a "nice to have" after all your work on the mountain, rather than a necessity.

Trekking into Everest base camp with the climbers
On both years we had people accompanying us on the trek to Everest base camp.  I think it's good having people trek in with you.  I know that my two brothers who came in with me in 2007 were a little concerned about how the other climbers would react and if they would be able to keep up.  A few extra people makes no difference (different faces from the ones that you are going to spend the next 2 months with are good too) and any sensible climber wants to get into BC in the best possible shape, so this means going in nice and slowly.  In both years we went in slower than most trekking groups.

The prices charged by IMG and Asian Trekking are significantly different - at the time of writing Asian Trekking was about US$1000 for everything in Nepal, whereas IMG are US$3950 for a Spring trek.  Mark Tucker from IMG was very good with explaining to the trekkers about altitude sickness, whereas I didn't see this coming from Pertemba in 2007 as much.  However I should add that the people who accompanied us on our trek in 2007 were all family members of climbers, so they tended to turn to us for advice.  With IMG we had some friends and family of the climbers, and some people who just came for the trek.  Mark Tucker did a great job of helping those trekkers who felt less comfortable and offering them some basic advice and assistance (that anyone attempting to climb Mt Everest wouldn't need).