When two of my priorities are transfer rate and Linux compatibility, which would be best to go with? Slots are very precious on my box right now, but I'd make room if USB is just a lot of trouble.

Also, is it worth it to get a G compatible if your ISP network is B?

There are more compatible PCI cards than USB devices, and generally if they work they will be supported directly.

However, you can generally get the USB ones working (Atmel or Zyxel chipsets are ones I've gotten to work myself), and as you note it will save you some internal space. Not to mention give you some flexibility to move the device around to get a better signal if necessary.

Given the average ISP, you're going to get at most 6mbps down, which means either type of card will support as much bandwidth as you're going to get.

FWIW,
Ewan

---

You can see my blog here. Whether you should is a different question