The best of the major tubes for work with is youporn - they have their own set of rules for editing of clips, adding logos etc, but they're responsive, cooperative, and generally worth the trouble. Average CTR is 0.5-1%, average ratio 1:1000-2000. You won't get rich posting there, but it's nice source of steady income and good branding, if you have enough clips to post regularly.
They also provide you with the nice clean banner space plus text descriptions. With youporn you basically run your campaigh yourself, which is not so with other major tubes and helps a great deal to work on improving conversions.
Second best is redtube - they post less stuff (only 20 clips/day) and it is harder to get listed, their CMS cannot handle large amount of sites etc, their watermarking rules are different from youporn and you need to reendcode clips, they provide banner links but banner spots are not that clean and they do not allow text descriptions. They also do not regard their content partnership program as their priority, thus you need to actively push them to get your clips sumbitted etc. All in all, they're not that easy to work with as youporn, but their conversion rates and traffic and CTRs are about the same and worth the trouble too if you can submit enough clips.
Those two, youporn and redtube, are the only 100% legit among the major tubes, which makes a huge difference when it comes to planning of your campaign - you can be sure that some sick fuck will not submit full length clip the same day you submitted 4 mins edited version of it and post it without banners, links back etc.
I also tried xvideos, but they proved to be next to impossible to work with. They post whatever is uploaded the same or the other day, thus you can't submit 30-50 clips to later post them daily for the next month or so. I didn't know this when I started, uploaded 50 clips and they posted them ALL within 1 day. That's sick. Add to that several of the same clips posted the same day illegally
But, to my surprise, ratios were although bad, but not completely out of this world either - about 1/3000. They do not provide banner space and text descriptions at all, only a small clickable link that is buried amongh cam and dating site ads and is barely visible.
Hhamster introduced their content partnership program not so long ago - I've sumbitted a couple of clips for tests but forgot to check the results so can't say anything meaningful about it. The only thing sure is that it is quite similar to the one of xvideos - you cannot be guaranteed from the same clips sumbitted illegally, they provide links that are so small they're more of insult for content owners rather than advertising etc.
I'm also seeing more and more legally submitted clips at pornhub, but as long as I know they sell spots, not just provide them 50/50 or PPS. Not sure if buying spots is justified, especially if you're expected to provide revshare or PPS on top of it. For volume submitters probably it is (though your profit margins will be rediculously low, if any at all), but not if you're only going to submit several clips. They only provide banner spot, no text link and your banner will be buried among dating ads and some loosy design elements that attract more attention than the banner itself.
Tube8 always had some kind of content partnership program, but it is hard to get there because it's not their priority, they only provide small text links, spots are limited etc.
Basically, from my experience, major tubes are not that horrible to work with as people often think they are, and even ratios and sales are not that bad, although they're not a goldmine either. If you have enough sites, enough clips, enough time and enough energy, you'll be pulling about 100-200 signups/month if you regularly submit to the major alexa top 100 tubes mentioned above. If you only have one site and 20-30 clips to submit, working with them is probably not worth it time/money wise unless your site and clips are really unique.