Currently, I'm using LimeProxies, and haven't had any complaints. My plan is for 500 private proxies (YouTube and Twitter), and I haven't had any problems with them: they are quick, and I get good upload speeds. Can switch my IPs each month, and they also verify that the new IPs are not banned with Twitter or Youtube each time I switch.
And I agree with the post about private vs public. There is absolutely no way to compare them. Private are more expensive (I spend a LOT on private proxies each much, but I'm pulling several thousand a month off that particular portion of my IM, so I'm not worried), but much, much better than public. With private proxies, I know I'm not going to get myself banned (I have about a .5% ban rate), so I don't have to worry about a chunk of other people.
If you're wanting to go on the cheap, try HideMyAss. They have a daily proxy list that is emailed to you with fresh public proxies for $24.95 lifetime. Don't expect them to have staying power for the whole day as they are going to be massively abused.