The selection of blade length really boils down to personal preference. There is a very wide variance of blade length preference amongst professionals. As a student develops, he or she may want to experiment with progressively longer blades, but when breath and embouchure support are fully developed, there will probably be a blade length that "feels" the best. A longer blade necessarily has a thicker profile, and generally requires more embouchure and breath support. A similar (but not identical) effect can be obtained by using a larger tip opening with a shorter blade. If the blade length is too long for the player, there will be a tendency to reduce the tip opening to a degree that causes the reed to be inflexible, especially in dynamic range. Conversely, if the blade length is too short, there will be a tendency to adjust the tip opening to be too large, causing soft playing to be difficult.

The main concern in the selection of tube length should be how well it matches the instrument and bocal. Each of the three tube lengths have roughly the same internal volume, so the pitch level will be very close to the same. However, the differences in the proportioning of this internal volume will effect the evenness of the scale, both tuning-wise and timbre-wise. In my opinion, there is only a slight difference in the feel of a particular reed model when one tube length is substituted for another: the shorter tube lengths may require a tiny bit more embouchure and breath support due to being wider at the blade wire. This difference is much less than using a blade length 1mm longer, and can be compensated for by using a tip opening that is marginally smaller. As of yet, I have not been able to come up with even the crudest rule of thumb to match a tube length to an instrument/bocal combination. Unless you have a strong opinion otherwise, my reccommendation is to use the medium tube length, settle on the other features (profile style, blade length, tip extension, etc.), then try the other tube lengths if you suspect that the evenness of scale could be improved.