I have personally never used SEOClerk but I have heard mixed opinions about this website. There are some good services there, but some are either going to do more harm than good or they are just preying to take your money and do not deliver. If you are using it for adult, I would not use it because they will give you low quality backlinks and I can say that just by looking at their offers.

I have used LinkSpun before when it was in its prime but now there are not many webmasters that offer something good, so I very rarely come there, but if you are new, you might find something there. After all it is free and if you do not have much to invest into links, you might try them out and maybe you will find something good.