One more comment about senior playing ahead of junior. First off, I don't have that situation so it is not some personal philosophy hoping to keep my kid on the field. As for two players being equal, this almost never happens so the argument is somewhat hypothetical. Assuming that is the case, I would still play the senior as I believe this would be the most beneficial to the program. I understand the concept of allowing the junior additional development and contributing more next season, but I also see making the junior continue to work to gain a spot, whether permanent or part time. If you pass on the senior, my experience is that that senior is probably not going to be the best person to then push the junior to improve. I personally do not think you can easily strip out high school dynamics from most high school baseball programs. There may be some ultra-competitive schools where high school dynamics has zero impact on the program, but for 95% of high school programs, this is the case.
I have seen where there might be a freshman that should be on the varsity team, but in very few case is that freshman going to be able to deal with getting put into that situaion. Sure, if he is on the field and the ball gets hit to him, he will probably make the play. But, sitting in the dugout next to some guys 3-4 years older than him having their usual conversation (and all the other athletic and social interactions) is not something that will benefit the team in the long run.
I am trying to make the factual argument that playing the senior can be a better choice, not saying the senior plays based on seniority alone. If anyone disagrees, please feel free to comment (and give some insight into how this impacts the team when the senior - who in this argument is just as good 100% across the board - gets dumped in favor of the younger player). If anyone feels like throwing out the participation trophy argument again, please save the effort for a more appropriate time.
I can see both sides from a purely competitive standpoint, but simply see more benefit in going with the senior.