Yes, I do agree with Karn, they are unreliable and stable.
Eg. My regular ping is 250 in SG. And about in random moments, it goes down to 110 (YAAAAAAAAAAAAAAAAAAAAAAAY!), then after 3 seconds, 350..(BOOOO!) then back to 250. :/
Usually SG servers are used, I have greater ping in JP (180)...