Hi!
The "Posh" hotel thing is a problem. In my opinion, there is not one anywhere in Kenya or Tanzania. I guess it depends on your definition.
Dar IS safer than Nairobi. It is also a lot more hot and humid. It will be quite hot and muggy in Dar, so that may sway your decision. Nairobi is never too hot, and usually pretty nice. NBO and DAR are both definitely 3rd world.
The best hotels in each city are downtown, not too far from the airports, but traffic is a big ??? If traffic is horrible, it takes a LONG time to get from downtown to the airport, in both cases.
NBO:
It sounds like this IS the best choice in NBO, and if you get a suite, does sound actually "Posh"
Tribe - the Village Market Hotel (Nairobi, Kenya) - Hotel Reviews - TripAdvisor
The Village Market area is the ONLY one that I've seen that I would say is really, really nice. I was actually shocked when I went there at how many Mzungus were there. It seemed like I had gotten lost in NBO, and somewhere fallen into a crack in the fabric of space-time, and had been instantaneously transported to Europe. It is very close to both the US and Canuckian embassies.
I do NOT think they would like the Stanley Hotel, which is very famous. Old and small rooms, like a typical big-city hotel that was built 100+ years ago.
Oh, and before I forget, I would NOT waste my time at the Carnivore restaurant. It is very unique-looking, but their exotic meats include Turkey and Ostrich...I can get WAY better than that in KGRB. The food is not prepared that well, and it is a huge waste of money. They are resting on their laurels from 50 years back.
I would recommend Haandi, a great Indian restaurant, or the Blue Nile, which has great Ethiopian food, if they want to try something a lot different than they normally experience.
Dar:
After thinking about it, I would stay stop in NBO. It is THE best African city between Cairo and South Africa. Unless they want the beach and hot weather....or you could stop at NBO one way, and DAR the other. NBO is bigger, and is THE main transportation hub for central Africa.
Don't know about the handler situation...NBO U can fly to Jomo or Wilson. Clinton, and top gov't people fly into Jomo Kenyatta. Wison is the old city airport, and is much closer to downtown. I am 90% sure that security is a lot better at Jomo Kenyatta. Oh, also, Wilson has no approaches, and to Jomo you can get radar vectored to the ILS 06.
cliff
NBO