As stated above me, your Ping value is a function of the internet speed of your connection combined with where you are in the world compared to the server with which you are trying to connect.
So as far as location is concerned if you happen to be in Asia or Australia and are trying to connect to North America then you will have high Ping values and there's no avoiding that. You definitely want to use the region with the lowest value, but if you happen to be in one of the aforementioned areas (which also seem to have the lowest player counts sometimes) then you may have to tolerate a certain amount of latency to enjoy a more active playing community.
Your Internet connection speed can also be a factor; if you have a lower speed on your connection then you'll likely experience issues, especially if you try to act as Group Leader or host a game in Ops. I have a few people I play with who have no issues when playing alone but who suffer terrible latency issues when they have visitors in their Backyard or if they are hosting an Ops game; likewise I'm been in several Ops games which work fine with no latency with 2 or 3 players in it but the minute Player 4 joins everyone involved suffers terrible lag because the Host/Group Leader does not have a connection speed which can handle that much demand.
You also can't forget that completely random factors happening somewhere along the connection between you and the server, or server issues themselves, can impact your Ping value. I have a normal Ping between 15 and 30 when connecting to North America East but there have been random times over the last year when that value has jumped well over 130 and once even over 200 due to unknown factors which didn't have anything to do with my connection directly.