How do you choose which pool to use, is it based on the pool hashrate or connected miners??
They're all going to be very similar. In the long-term hashrate doesn't matter so much, as theoretically, the end results should be the same. A pool with a higher hashrate will get you more frequent but smaller payments, where a pool with a low hashrate will get you less frequent but higher payments.
Pool fees may be a factor to look at, but in Bipcoin's case the difference between 1% and 1.5% isn't huge.
Payment threshold is also something to consider. They range from paying out when your balance reaches 0.1 BIP to 5.0. If you're mining with a small hashrate, you might avoid the higher payment thresholds
Reliability is another thing to consider. You'll want to watch the logs when trying out a new pool. I have connection problems with one of the pools, but it might be caused by geographic location rather than something wrong with the pool.
Lately, I've been using both cryptonotepool.com and bip.crypto-coins.club. If your mining software supports multiple pools for failover, definitely use that feature.