How to prioritize what access point my wifi connects to?
With your setup of multiple access points sharing the same SSID (network name), your wifi client will use its built-in roaming algorithm to switch. But even if you have a marginal signal (i.e. one bar) on the one that's farther away, most times, the wifi client will stick to that access point, simply because it was the first one configured. To get around this you have two options...


Use different SSID's, and in the Advanced section in Network Preferences/Wi-Fi, drag/drop them in the preferred order. The good thing about this is the ability to quickly see which one you're connected to at any time and explicitly switch over whenever you want.
If you must have the same SSID... Change the SSID for the closer (desired) access point to a new name (e.g. "NewName"), re-associate your computer to that access point with the new name, then change SSID for the older access point to the same new name.