1st violin parts are typically more "difficult" in the way that students and amateurs are likely to use the term -- often a lot more notes, and in higher registers, and often with greater complexity.
2nd violin parts are primarily harmony, which means the finger patterns are less common and less intuitive, the rhythms are often trickier, and you sometimes need to really focus on what you're doing because of repetitive patterns and the like. And there's often less for the ear to hold onto, thanks to the lack of melody.
Sincerely,
The Violas
(2nds will usually have harder rhythm, 1sts the tunes and harder/higher notes. Depends which you are weaker at which is harder)
Mary Ellen, some of Mozart's "German Dances" were composed for village bands, at least one of which apparently lacked a violist. Mozart accordingly would write an elaborate 2nd violin part to make up the deficit, a part more "difficult" but perhaps more interesting than the straightforward dance tune of the 1st violin part.
As with all group activities there tend to be a lot more support personnel than front line people.
That may be the reason that many musicians love chamber music - a good chamber piece moves the melody around so everyone gets a shot at leading the melodic structure while the others provide support.
As I mentioned, I liked sitting in the second section. It taught me to count, pay attention, listen to others, and never to get a swelled head.
These days both scores and professional performances are readily available online, it is easier to learn the musician-ship part of the job. All else being equal, the challenges of first violins are greater.
If one is dealing with Hindemith's Nobilissima Visione or Ligeti's Le Grand Macabre then difficulty is really measured only relative to the individual player's skills.
I think my weakness is partially due to being a good violinist as a youngster. The better violins were always firsts. I didn't play 2nd violin at all until I went to college, and that was just in one orchestra. It's harder to play 16 measures of repeating eighth notes with musicality and perfect rhythm than it is to play a melody any day of the week.