Personally for me it's a matter of whether you want colorful aggressive fish that spend their time chasing one another around, calling for overstocking to avoid the loss of all but the most dominant, but very owner responsive ( Malawi Mbunas ). Peacocks make a nice display ( espescially all male setups but if you want to breed you'll have one to two colorful males per 4-6 drab females.
If you like to watch fish act naturally and pay little mind to the outside goings on, or fish that won't tear up your plants, go with Tanganyikan. They are not usually as colorful as their Malawi cousins but make up for it in personality and odd behavior/ body shapes.
You'd probably do best to start with Mbuna as Coler as mentioned. They are relatively inexpensive and will fill a tank with color. Down the road you may make the switch to Tangs as the pretty colors of the Mbuna become less important as the interesting behaviors of other Africans.
As has been mentioned, water parameters out of your tap should make your choice for you. I keep Tangs in 8.6 pH. I wouldn't try much less than 8.2- 8.4. This can sometimes be achieved with the use of crushed coral or other limestone type rocks, substrate. If your pH is below 8.2, or the tank is not seasoned ( 6 months seems about right for most of the more sensitive Tangs ), go with Mbuna. I honestly don't have enough experience with Vics as they are rare and I have not had the occasion to keep them.