Adsense for sure. You asked which one is more reliable. Forex is not reliable - you can lose as much as you can win. In fact, the chances of losing money as a newbie in the Forex markets are much greater than the chances of winning. L.E. Unless by Forex you meant opening a Forex blog/news site/etc and monetizing that through Forex affiliate networks.
Forex is my forte here... it's much more about psychology than dried in the wool "methods". You know, most methods actually do work. But people don't implement them, they always get trigger hapy and trade emotionally. As usual the difficulty doesn't lie in the task but in controlling yourself and constantly improving..
Google Adsense is easier way of earning as compared to Forex trading. Forex allows you to earn unlimited money but the problem is that you need an experience.
In my opinion between the two adsense and forex two different jobs that rely more on performance andsense our website while the analysis forex stock market in the world, especially in Europe, both equally benefit all depends on his own you want to select which if adsense is more simple forex technical depth and analytical needs that fit ..
Adsense is guaranteed earnings without risk. Forex is extremely dangerous if you do not know the basics of Forex. Especially with leverage up to 500x given by some of the Forex brokers. That is tremendous risk.