For the bandwidth and latency, it all depends which version of Bluetooth both your phone and your computer support, and what kind of network connection you're tethering. Your connection speed will only be as fast as the fastest standard supprted by both devices.
From Wikipedia's Bluetooth page these are the theoretical maximum speeds for various Bluetooth versions:
Bluetooth Basic Rate (BR) 1Mbit/s
Bluetooth 2 Enhanced Data Rate (EDR)
Bluetooth 3 + HS (high Speed) 24MBit/s
Whereas for Wi-Fi (again depending on the Wifi version supported by your phone and your Mac:
IEEE 802.11b 11 Mbit/s (realistically 5-7MBit/s)
802.11a 54MBit/s (realistically around 20 Mbit/s)
IEEE 802.11g 54MBit/s (realistically around 20 Mbit/s)
IEEE 802.11n 54MBit/s to 600MBit/s
(most devices these days support B & G, with new, fast devices supporting N as well)
So on the face of it, Wifi will normally give you a faster connection. However if you're tethering your phone to your Mac to connect to your phone network's data then the limitation is probably going to be the speed of your phone's data connection.
3G isn't a precise term and means different things on different phone networks, but you're normally looking at a speed of around 400Kbit/s to 2Mbit/s, which means that anything better than Bluetooth Basic Rate ought to be able to carry that data speed pretty comfortably.
HSDPA aka 3.5G supports speeds of between 2MBit/s to 14MBit/s (depending on the implementation) so if you have a decent HSDPA or HSPA+ signal then you are probably better off using Wifi.