1) 100 is noticeable over 10
2) Switch is better, although if you've only got 2 PC's it won't be noticeable. The difference is that the packets get repeated out ALL ports on a hub, but only get repeated out the destination MAC address port on a switch, thereby reducing collision potential. So the more machines on the LAN the better a switch would be vs. a hub.
If the switch is only a bit more expensive than the hub, go with the switch.
<i>It's always the one thing you never suspected.</i>