Feb/Mar should be hot and dry in Kenya/Tz. Apr/May is considered the long rains season but it's hard to predict the weather anymore. Apr/May would also be less crowded with lower prices.

Can't comment on Southern Africa weather.

If this is first and only trip, then I recommend Tanzania and or kenya during early 2013. It is 'As Seen On TV'. Like Patty said, may is half price usually, try to go around may end and save some. If you want to see the migrating herds in Southern Serengeti, then feb-march.

February or early March would be a great time to visit Tanzania. The Migration herds are usually in the southern Serengeti then, dropping calves.

To do South Africa - CPT, Kruger along with Vic Falls and maybe Chobe, lots of internal flights... Visa for Zimbabwe (VFA) and Chobe in Botswana.

If Tanzania, Feb would be great for the 'calving' of the wildebeest in the Southern Serengeti/Ndutu areas, but at this late date space maybe hard to come by. March would be a better bet if interested and space more likely... the herds are still around the area thru April.

Kenya is also good Jan-Feb, though the migration won't arrive till July, game is a plenty everywhere (there's nowhere else for them to go) and prices will be lower than if in Tanzania. Both countries require Visas for entry.

While Apr/May are considered the 'long'rains, if it does it won't be daily, all day... maybe a brief amazing thunderstorm or shower at night/morning. Besides prices are at 'low' season and with any wet, all will be green, and there are baby animals, all species... it's springtime!

Tanzania and/or Kenya can be done as 'all' driving safaris with a flight from farthest distance back to start point, or if in Kenya, depending on where visiting can include a few other short-haul flights.

I'd go with East Africa, either country where the daytime temps will be warm to hot and dry, evenings/mornings always cooler; even if some rain, rare for there to be humidity after.

Good luck with your decision.

For me, it would be a contest between Tanzania and South Africa, excluding Kenya. Your question leaves a lot of unknowns, such as whether you intend to put your travel plans completely in the hands of a competent travel agent or try to arrange it by yourself. You don't mention how long you intend to be in Africa. Also, we don't get any idea of your interests: animals, culture, broad view of life in an African nation (quite different in the three countries you mention), hedonistic pleasure, or something else. I have long thought that, for the first trip to Africa (and, I doubt that, once you go, you won't find a way to return), a visitor should first consider South Africa because of the developed infrastructure for tourism, the use of English as a first language, the diversity of the nation, the many attractions available to visitors, and the great beauty of the country. In the prospective itinerary that you allude to, I'd like to see a little more finesse. I give a thumbs up for Cape Town and Victoria Falls, but I would like to see more development of your plans. There are many other places in South Africa to visit than Kruger and Chobe. Every tourist knows about them. How about the equally significant but lesser known? ZZ

P.S. I see that I misspoke in my first response. Of course I know that Chobe is not in RSA, but, if you're going to Vic Falls, that becomes a feasible option. You could save a lot of money by concentrating on just South Africa and omitting the other destinations. ZZ

For a true safari experience, Tanzania is so much better than South Africa for exactly the reasons Zambezi lists as "pluses" for S.A. and which I consider "minuses" for a safari: lots of development (also fenced reserves, thick bush and less wildlife.) Having been to both countries in the last year, I'd recommend Tanzania over S.A for your first safari. English is also spoken everywhere in Tanzania, you'll get to experience a wide variety of cultures including the Maasai, see the beauty of the Ngorongoro Crater and the classic "Out of Africa" vistas of the Serengeti. South Africa is an interesting country, but you go there for a "taste" of safari in addition to the other sights like Cape Town and the Garden Route.

We are looking at African Adventure tour for S.A. and either OAT or a much more costly college alum trip for Tanzania. I wish I knew that we would be going more than once, but can't count on it. We have a very long bucket list of other places to visit.

Apparently both are 'group' departures, with set dates, routing (often not the best place to be time of year dependent) and set accommodations. Nothing wrong with group departures, but you'll find many here prefer a 'private' safari, designed to meet your wishes, travel dates that work for you, selecting own accommodations and keeping budget in mind. Decisions on safari made by you that a group of strangers often with different interests.

Why not provide the links to each of these itineraries (including the Alum trip... these are unfortunately often more costly, but for what reason? maybe they send a Tour Director with and guess who pays? or the university has to make a profit), so we can comment whether worthwhile/cost effective, etc.

OAT's "Safari Serengeti" is a fairly good safari for the price (especially since it includes your airfare from the US.) You say that there are 6 of you. OAT does "private departures" if you have 8. You might see if you can round up another 2 people and check with them on pricing. 8 is also a good number for a private group (4 people each in two vehicles.) My safari planner of choice is Bill Given of "The Wild Source". He has an incredible guide in Deo Magoye and they are setting up their own outfitting company in Tanzania. You could also get a quote from him. It will be higher than OAT, but you can design the safari the way you want it to be. As you say, this might be your only safari and want to do it right.

Depends a lot on what you want to see.
If it the classic African plains/savannah, then you want Kenya or Tanzania.
I fit is the big 5 up close, personal, and often, then it is South Africa.
Here is a pro photgraphers evaluation of them. (Go about 1/4 way down just past the lion photos). But note his primary interest is photography.
http://www.bythom.com/botswanaworkshop2.htm

regards - tom

My vote would be for Kenya/Tanzania where you can get both the wildlife and the culture of East Africa. South Africa is beautiful of course, but further north you get the sense of the "Real Africa"
And I agree with Sandi, private safaris are a better option. Especially if there are six of you already, it cannot be so much more expensive to book a private tour.