Hydration Pack/Vest?

Hello! I am new to trail running. I am using it as a way to get out on trail more and train for backpacking trips. I am also looking at training for some races.

I am wanting a hydration vest/pack that can be used for a mix of shorter trail runs and longer runs/day hikes and can be used for some half marathon distance races. Kind of a do it all pack.

I am looking at the Black Diamond Distance 8. They have a sale on past models. Any other recommendations or advice? Or should I go the distance 15? Is 15 L too big?