"What's the difference between Auto and Manual Traffic Exchanges?"
Here is what I know:
Auto Traffic Exchanges are used to deliver high quantity traffic to webpages. The benefit behind this strategy is solely to increase traffic ranking with sites such Alexa, Compete and Quantcast. The higher the ranking, the better chance of exposures on the search engines. If you run an e-commerce site or a site that rely's on member signups, then the auto exchanges are not for you. Auto exchanges require minimal participation from its surfers.
Manual Traffic Exchanges require the surfer to view timed ads. In order to advance onto the next ad the surfer needs to click on an appropriate link. User participation is required to the chances that the surfer might find your ad interesting are high. Its is possible that you might generate a sale or a member signup. I submit referral links to manual traffic exchanges in order to grow my downline. Manual sites are very effective for these tactics. Most manual exchanges are theme related and offer the surfer a fun surf experience.
Both Auto and Manual Exchanges offer a free signup with the possibilty to upgrade your account for close to nothing. If you run out of credits, you can buy additional credits. Some exchanges allow their premium subscribers to sell their credits back to the exchange. All offer bonuses to members who promote their exchanges with the use of referral link, splash pages and banners. Most exchanges generate prizes for their surfers to find while they surf and some exchanges reward their top surfers through surfing contest.
Now that I got that out of the way im going to introduce some exchanges that i have tested and have proven their worth.