You should stick with as few bridges as possible. Assuming that some are run by our adversaries, the more bridges you "sample", the more likely you are to get on someone's list. Bridges are supposed to be for censored users in places like China and Iran. No western countries block access to Tor, so you gotta figure that local bridge users will be interesting to LE in these countries. Trying to hide their Tor use, they must be up to no good. So it's entirely possible that they are running some bridges and enumerating the IP addresses that connect to them. To mitigate that attack, connect to as few as possible.