The album-wise comparison of the BBs and J&D:

[Steve Latshaw]

Jan & Dean were fast friends with the Beach Boys.  A genuine bond, there... much in common.  And the Beach Boys were huge J&D fans, particularly Mike and Brian.  The Beach Boys' "Surfin'" is more of a J&D song, in terms of the bomps, etc., than a Beach Boys songs, in regards to style.  The Beach Boys were genuinely in awe of the duo, particularly when they were asked to back them up - and then J&D offered to sing their songs live on stage and in the studio.  It became a working partnership... Brian helped Jan with great songwriting and singing (Brian is all over Drag City, Deadman's Curve, etc.)... and Jan helped educate Brian in studio technique.  But they were all great friends, and continued to be throughout the years.

I think the only rivalries were between Liberty and Capitol and Jan & Murray.

[relx]

Mike and Dean are still good friends to this day.

Jan and Dean's early success actually predates the BB's existence by several years. "Jennie Lee" (Jan and Arnie to be technical) was a top 10 hit in 1958, three years before the BB's got started, and "Baby Talk" was a hit in 1959. Jan and Dean were already an established act when the BB's cut "Surfin."