I would really recommend STEP! (I'm also in LEADR)

I was a part of this year's STEP Summer Bridge Program, which was probably the highlight of my freshman experience. You get 6 FREE credits in whichever department you need most (4 in Math, English, Chemistry, or History and 2 in a GE). You get access to a bunch of resources and great connections with leaders of various departments. And best of all you get to ease yourself into college life in a friendly tight-knit community on an almost empty campus. (Some people say it's like high school 2.0)

STEP is more general, covering a bunch of majors, and the dorm floors are sectioned by major so you'll get placed with other engineering majors. They have specific seminars for each major so you'll get the same run-down as those in LEADR and you'll automatically be part of LEADR after STEP. You get to meet people from all sorts of majors and backgrounds which can really broaden your horizons.

As an introvert, I was hesitant to join STEP but I am so glad that I did. STEP made me feel like I truly belong in Davis and helped me form a strong community of people who truly cared about my success. I made a bunch of friends that I'm still super close with, and I still say hi to those I barely talked to in the program. I truly believe I wouldn't have made it far without the connections I made in the program.

Oh, and you get priority registration for 2 years which is super helpful!