Deadhorse - I trekked as a FIT (free-independent-trekker, in Nepal trekking terms - no guide, no porter) to EBC a couple years ago as part of the 3-passes trek in the Khumbu region. If you're considering whether to go solo or guided, there are definitely some big pros and cons to consider beyond the obvious cost and pack weight issues:
*Flexibility - as a FIT, you can wait out a day or two of bad weather, spend an extra day acclimatizing, or add a last minute side trip to Ama Dablam basecamp if you choose. As a part of a guided group, you have no such flexibility, and it could easily cost you a highlight of the trip (missing Kala Pattar due to clouds, for example).
*Lodging - as a FIT on the very popular EBC route, you will be treated as the absolute lowest priority client by guesthouse owners. The owners want repeat business - the highest priority will go to guided groups, then solo trekkers with guides, then solo trekkers with porters, then finally FIT trekkers. Of the 20 nights I spent at altitude, I got kicked out of various rooms (politely, at least) 3 times so they could make space for guided groups. It didn't matter that I had already taken the room and unpacked - they asked for the key back and pointed me to a lodge that had space. At least 4 other FIT trekkers I met experienced this same problem. It's not a huge deal since you can always just go next door to another teahouse, but it's still a pain. Note that this was only happening on the popular route to EBC - no one on the Gokyo side experienced this while I was there.
*Flights/Permits - it's not all that difficult, but definitely an effort, to arrange permits and flights as a FIT. At least you can book flights ahead of time, but you still have to make a face-to-face visit with an agent to pick-up tickets. Permits must also be picked up face-to-face at an official TAAN location. Also, changing your flights due to weather, change in plans, etc., can also be a pain as a FIT. If you are on a guided trip, the guides will coordinate any and all permits, flights, changes to your flights, etc. If you are a FIT, you're going to be spending a few hours running around between the airlines offices and TAAN offices trying to sort things out with the less-than-pleasant airline and govt. workers. Also, FITs generally get lowest priority on flight changes.
That said, for me, the whole point of going to see the Khumbu region was to see the sights and I didn't want to be tied to a rigid schedule, so I wasn't going to do it any other way than as a FIT, but I can also understand why guided trips may appeal to some, esp. anyone that hates planning.
Finally, if you want to see Everest but aren't married to the EBC trek, I would highly recommend going up the Gokyo valley instead. It's more beautiful, far less crowded, and you get a better view of Everest (although from further away). And nowhere on the EBC trail will you be able to see 4 of the 6 tallest mountains in the world (Everest, Lhotse, Makalu, Cho Oyu) at once, like you can from the top of Gokyo Ri. Also, if you're going in the fall, note that there actually is not a base camp at Everest most years in the fall - they setup a fake 'welcome to everest base camp!' sign on the tourist side of the icefall so the fall peak crowds don't endanger themselves trying to cross the glacier to visit something that isn't there.
So...back to the original question, I don't actually have any experience with any specific trekking agency since I did the trek as a FIT, but hopefully the above will be somewhat useful if you're still trying to decide what to do...