Santa Cruz Vala C MX 90 - 2027

Find your Size
If you're on the cusp between the recommended height range of two sizes, the absolute best thing is to try to ride them both. At a minimum, check the stack/reach measurements on your current bike and compare it to the new model you are looking at to get an idea of a fit you are already comfortable with. If riding the bike is not an option, consider the following.

Personal Preference
A larger size frame will be more stable, and will give you more room to move without upsetting the weight-balance of the bike. The larger size will put the front wheel further in front of you, which gives the feeling of security and conversely, it will require more significant body movements when you WANT to shift the weight-bias of the bike. Think hard about your riding style and how active/intuitive you want it to be vs stable and speedy. You'll need to work a bit harder to muscle the larger bike around.