Wireless signal can get weakened by EM interference from other devices operating at the same frequency, such as phones. Also, the location of the access point and the router capabilities are very important. I've used routers where the signal travelled beautifully all over, but I've also had some could barely transmit outside the room they were located in.
But wireless is very convenient, you can move around, let multiple users connect etc.
Stick to wireless but take a few precautions:
1) Use WPA security and apply a strong, non-dictionary password. Dont even think of using WEP.
2) It is generally advised to place the router somewhat high up from the ground level.
3) Get the best router you can within your budget, it makes a lot of difference.