Wifi speed up, down, all over the place!

Every day this comcast device has to be reset to get any sort of decent wifi connection.  Sure, I am running over wifi, but who isn't?  Comcast says that it's "your issue" if you are not harwired to thier modem, router, or whatever this is.  Anyone have any ideas why this wifi is "SUCH A BAD WORD" on goth 2.4 and 5?  I don't want to walk around with a cable attached to me everywhere.  Thanks!