We recently stayed at the Onsea House/Machewo and it was wonderful! The owners were very helpful and accommodating. Although I had read earlier reviews of the rudeness of the owners, we never found that at all. Our flight arrived around 1 AM at Kilimanjaro Airport, and did not really arrive until around 2 AM. People were there to let us in the gate as well as provide us cool towels and a lovely welcome juice drink. Staff were very accommodating and responsive to our needs. The rooms at Machewo were perfect for us with a nice lay out and real shower. As an internet addict, the WiFi was great and very fast (much faster than what we got later in the bush). It was a nice play to lay over for two nights prior to our safari. The pool area was lovely as were the great views from the rooms and restaurant. Personally, I loved the location of the Onsea (away from the city which really was a little too busy for me).
We also went to Arusha National Park one day and that was a really wonderful surprise with a lot of animals and very green and lush surroundings. We were lucky, too, to get a great view on a day trip of Kilimanjaro. I cannot say enough. My only complaint (minor) is the food in the restaurant was very good but not consistent. That may well have been because the chef had a broken wrist and could not do all of the cooking. I would highly recommend staying here--perfect way to start or end a trip to Tanzania.