Wires are much Quicker with High Performance Tasks.
Typical High-Speed Consumer ADSL Connection 512kbps (Peak)
10BaseT 10Mbps (Mega bits per second) Peak
802.11b 11Mbps Theoretical Peak (Dependent on RF Noise)
802.11g 54Mbps Theoretical Peak (Dependent on RF Noise)
100BaseT 100Mbps Peak
Wired networks are more stable, and more likely to constantly be at Peak Performance. Wireless networks can fluctuate significantly, and some people still claim that 802.11g can't reach the 54Mbps at all! Latency is also a Problem.
Taking that into consideration, if you're only using your LAN to connect to the Internet, even Noisy 802.11b will be much quicker than your ADSL, so it's not gonna cause any degradation of speed. If you use your LAN for data Storage, or for high-volume, low-latency transfer of data (Local File Sharing, HD Video, High Performance LAN games), Wires are definitely a much better idea.