Should I master Russian or French next?

Hey guys! Today I have quite the dilemma.

As some of you may or may not know, I am actually bilingual in English and Spanish thanks to my Mexican American upbringing with my bilingual dad and my monolingual mom that only speaks Spanish. However, I've been interested in learning a new language just for fun. I got onto Duolingo initially to learn some Russian and my lessons have been doing well. I have a Russian score of 9 and my accuracy is an overall of 92%. My memorization is also really good and I've got the hang of most pronunciation but it's not exactly the same as that of a fluent Russian speaker.

Anyways, I found this book meant to teach the basics of French and it's currently sitting on my desk. Now I just have to know which language I should learn next. I mainly just want advice based off which language will be more challenging to master. I'm also interested in learning Italian but since some of the vocabulary is very similar to Spanish, I'm not too worried about trying to instantly learn it as my next language. Maybe I could learn Italian as my 4th language.

Any and all advice will be appreciated. Anyways, I'm going to go lie down in bed and finish watching Matilda but I will be back soon. Bye Bye!