What kind of recs are the most effective?

The best recommendations come from the people who know you the best - and the most effective strategy is to combine recommendations from people who have seen different aspects of who you are. Put together, admissions officers will then get a holistic view of you in and outside the classroom.

Recommendations from deans, professors, and alumni do not mean too much if those people cannot highlight the ways you shine in detail. Here is an example of when you would want to invite one of them to be your recommender:

Let's say that a school that you are applying for requires one rec from one of your high school teachers, and another from someone outside the classroom. Your high school biology teacher could talk about your intellectual curiosity and certain elements of your personality, but may not know too much about your extracurriculars, leadership, and motivation for applying to college. The alum you know well could touch on these aspects of who you are.

Hope this helps!

The most effective recommendations are from the people who have been able to see you grow and develop your own personal characteristics. For example if you were in scouting and participated in a lot of volunteering and leadership positions, a good source could be the scouting leader. Essentially you want to submit recommendation letters from people you think know you the best and can subjectively comment on how you have grown as a person. I hope this helps.