The easiest to use is the bus - it has a fixed route with clearly displayed numbers and a fixed price, which is always nice when you can't be faffed to bargain. The down side is that you need to want to go where the bus is going and you could be waiting for anything from 5 minutes to 2 hours!
Car rapides are more regular - they seem to be going all the time and they do have fixed prices and, apparently, fixed routes. The problem is that the routes aren't displayed so finding the right one can be an issue. But if you can figure out where they're going and you want to go there then you're golden. They're probably my favourite, or will be once I've worked out the routes, you feel like a proper local and less of a tourist if you use them which is lovely!
Taxis are ten-a-penny round here and good for if you want to go somewhere directly, rather than sticking to a pre-arranged route, but you do have to bargain for the price so you need to know about how much you ought to pay unless you want to be charged almost double for a trip! Also, it can be 'interesting' if you're going somewhere for the first time and aren't too sure where it is because the chances are that the driver will knwo the area but not the specifics and you could end up driving around for a while. Or course, one of the nice things about Senegal is that he'll end up just winding down the window and asking a passer-by who will invariably know and be immensly helpful! I do like taxis, although car rapide is still my favourite, but it's mainly in taxis that you get the full force of Senegalese window shopping. Not the same as window shopping in England; rather, every time the car stops or slows down <which is often in city traffic> you get many vendors at the window trying to sell you anything from underwear to car parts! So far all I've bought out of a window has been a bag of mandarin oranges but I've been offered many phone top up cards, chewing gum, cashew nuts and even light fixtures! It's a wonderful place:o)