Here's my take on them.
Musicality (from easiest to hardest - pertains to how difficult it is to make a quality interpretation of the piece, making it presentable and coherent to an audience, also memorization and harmonic issues)
Sonata 1
Sonata 3
Sonata 4
Sonata 2
Sonata 9
Sonata 5
Sonata 6
Sonata 10
Sonata 7
Sonata 8
Technicality (How complex rhythmically they are, notes per measure, velocity, finger dexterity , again from easiest to hardest)
Sonata 9
Sonata 4 (pretty close to 9)
Sonata 10
Sonata 2
Sonata 1
Sonata 3
Sonata 5
Sonata 8 (pretty close to 5)
Sonata 6
Sonata 7
So Overall, this is my (subjective) order of the comparative difficulty of the sonatas (from easiest to hardest):
Sonata 4
Sonata 9
Sonata 1
Sonata 2
Sonata 3
Sonata 5
Sonata 10
Sonata 6
Sonata 8
Sonata 7
So, why don't you learn the 4th sonata then? It's very beautiful, and certainly a crowd-pleaser.