There's no one "best" service. The performance varies dramically by domain name and by parking service. The income on one can be ten times that of another for a given domain, and the opposite for another.
Some work better for type-in traffic, some better when there are a lot of old links to a domain. Some are mainly to help you sell the domain, some are not intended to do that.
Sign up with several and try them out, to see how they work for your specific domains.
was looking into parking domains what do you recomend as the best and what to watch out for is your site tied in for a certain term
As to "term", there is an ICANN rule that you can only move from one registrar to another once every 60 days... so I guess that's the minimum "term" for domain which you want to register and park.
GoDaddy offers free custom parking page -- ($8.95 for domain registration no charge for parking page)...
Most important in my book is whether they intercept your traffic when you use the "free parking page"... some registrar and hosts will park you page -- but they list a bunch or "related searches" or advertise third parties on your parking page... (I don't mind a small "Parked at Host.foo" type notice -- but on a busy parked page, you may be losing out on ad revenue that is going to the host you paid for the parking space)....
The WW TOS favor not posting commercial promotional type links, such as "Widgets.com is the BEST domain parking service". Such posts tend to open the forum's doors to promtional spamming.
Do a search on the phrase "domain name forum" or "domain forum" and you will find your way to lengthy discussions about domain parking PPC programs. There are 3 or 4 major domain forums, each with 10s of 1000s of posts and lots of opinions and detail. If you can't find them on searching sticky me.
As you can see, this will not generate much if any income for an obscure domain name.
