I think that for a French speaker it is more difficult to achieve elementary to intermediate level in Russian than in German, but it makes very little difference in the long run. You will have to learn the cyrillic alphabet for Russian, of course. Both languages have tons of cases, so you will have to learn a lot of paradigms for any of them. Russian has difficult aspects like vowel interchange in different forms of the same word, but only three tenses. German is pretty consistent in how words decline, but has some crazy grammatical structures with fixed word order. Russian has free word order, which is easy on the one hand but can become a problem when your sentence suddenly changes its meaning when you phrase it slightly differently. And so on. Russian is my native language which I also have taught, and I was B2 in German when I last took a test. I think that above A2 it's a toss-up which is worse / more interesting. tl;dr Take the language you will have chance to practice more, they are both insane. If you don't have much free time, take German because it makes more sense at early stages.

I would think that Russian is more difficult.

I think it is Russian! That is true)