I went to Nepal with World Expeditions in November 1997, out to Gokyo. I cannot say that I found anything unsatisfactory about the trip and lots to be pleased about. I have no reason to believe they would have changed significantly, and would go with them again. (I have just come back from a trip to the Middle East with them and found everything as well organised as in Nepal. They even rang everyone in the group up with a detailed questionnaire about our experiences, and tell us they will be changing some things as a result of the feedback.)
Here are a few notes you might find helpful:
1. WE uses local companies to run its trips, so their Nepal trips are run by a company based in Kathmandu, but with WE supervision/training/etc. So, for example, the trip leaders are brought to Australia to be trained to a high level in medical issues so as to be able to recognise and treat problems before they become serious. (Each trip carries a medical kit equipped with a variety of drugs which the leader will dish out as necessary. Apart from anything else, this saves you having to invest in a variety of medications - at Australian prices - that you will probably not use anyway.)
2. The Everest region is mostly populated by Sherpas whereas Annapurna is a different racial group.
3. WE uses tents except in Kathmandu. They were carried by the porters and pitched for us each night, usually in the yard of a teahouse. Meals were all cooked by WE staff, and served either in a room in the teahouse or in a dining tent they erected. No-one in our group got serious diarrhoea, and mild cases were dealt with immediately.
4. All the equipment they provided was good quality. Mountain Designs alpine sleeping bags. Down jackets. The tents were large and quite warm - my mate and I slept with the door half open even when the temp was down as far as -11.
5. WE is very careful to minimise the effect of their trips on the somewhat fragile environment in Nepal. To that end, they are careful not to use local resources and carry most stuff in with them from Kathmandu, and any waste out again. They do not stay at places, for example, that offer hot showers made by burning the local timber. (When I was there, one place had a solar hot water heater. I would guess that they are fairly common now - does anyone know?)
6. Everything was included on the trek except souvenirs and snacks/drinks you bought. I think some meals were not included in Kathmandu.
7. If nothing else, it is a chance to get to know some new people often with similar interests to yourself.
8. Some of the other people have commented that they felt the company groups were too big. I didn't notice that particularly, as people all walk at a different pace and tended to spread out a bit so that you didn't see most of them again until you got to lunch or camp. Maybe they are thinking of the difficulties in making decisions in large groups? Not a problem with WE as most of the decisions have already been made for you.
9. We chose to go with a company because neither of us had been trekking before, and knew few people to ask for advice. Now of course, the Internet provides a wonderful resource to seek information as you have been doing. That said, there are stories all over the place about independent trekkers getting good local guides and getting bad local guides. Maybe it depends on how good you are at negotiating, or recognising whether people are genuine or not, or how much research you have done in advance. Going with a big company is a safe and easy option, albeit more expensive than organising your own trip.
10. In November, the weather was pretty stable. Mornings were often frosty, warming up to a "pleasant" 5-10 degrees by 9am. It was sunny then until the clouds rolled in about 1-2pm, when the temperature would take a rapid dive to close to zero. It caught me once. At home, if it turns cold, I just carry on with what I am doing, and get warm when I go inside. In Nepal, I made the mistake of doing that and got quite chilled without realising it. I suspect I was well on the way to hypothermia before I put on some more clothes.
11. Some useful health sites:
http://www.ciwec-clinic.com/http://www.himalayanrescue.org/hra/index.php (Very good section on altitude sickness)
12. One lady in our group got mild altitude sickness. She and her husband and one of the guides stayed two nights at one place, then caught up with the rest of the group the next day when the group stayed two nights at one place. (This is one case where you may have to pay more, as you have to pay for the extra night and the guide's wages until you catch up.)
13. I was fairly fit at the time, but found that even at Lukla (2860m - barely higher than Kosciusko), the thin air was noticeable. Exertion would have me puffing and panting. At higher altitudes like Gokyo, it was often a case of taking a step, taking 2 or three breaths, then taking the next step. It took a while to get used to this style of walking.
14. I know people who have travelled multiple times with WE and with Peregrine. There does not seem to be much to choose between them.
Hope this helps.