All of them have very fast service and excellent ticket response.
KnownHost is good however their network tends to spike a little at different times of the day so sometimes I get packetloss or high ping, shouldn't be a problem if people just want to host websites on them. Zone.net has been very good and stable and excellent support / service along with good network coverage.
I'm barely 1 month with Steadcom so I can't comment much on them but everything is good so far.
It sounds like your using our old California DC in San Jose. We sent an annoucement and have recently moved to a new DC which is 10x better in Los Angeles. You may want to make the move like many have already done. Just wanted to mention that.
I do already have existing providers, I'm just asking for more options as there is room for expansion pretty soonish. I'm looking CA providers as I have a lot of users from around the world and it seems CA gives the most centralized hosting for everyone of my clients although they are still mainly from SEA.