I love learning classical etudes to improve my technique, hand position, and musicianship. The books I've worked out of are:
Jim Stinnett's "12 Keys to Success". This helped me develop my technique and I learned about different shapes that are common in most music. I worked up a few of the etudes to fast speeds to improve endurance and chops. Like this: Fast Electric Bass Classical Etudes - Mike Dyer - YouTube
The other one I work out of is John Patitucci's "60 Melodic Etudes for Acoustic and Electric Bass". These seem more to focus on playing melodies accurately and developing more dynamics and articulation. I've only done these on electric bass as I'm not a great upright player. These have helped with hand position a lot too.
What classical etudes are ya'll working on? I've heard good things about Simandl and I have one of his books but have never dove into it a whole lot. I would love to get some advice about these and also get other recommendations for etudes that improve technique and hand position that are also fun to work on...