I would recommend German over French.
From an economic and technological standpoint, Germany is much more powerfull nation than France. This results in better job opportunities in the long-term if you are interested in working or studying abroad. Personally, I want to get my Ph.D at the University of Innsbruck in Austria so that is my personal motivation to learn German.
As for being more difficult, I personally don't think so. Both German and English are derived from the Germanic language. Because of this, they have many similarities. For example, sentence structure is very similar to English and there are several cognates. I have studied Spanish as well and I find German to be a much more enjoyable language.
Hope this helps.