While you are probably right about research opportunities are probably more available at UCSD, coming in as a transfer may make them harder to come by. Students admitted as freshmen have relationships with faculty/staff and other students that build over the 4 years, while you’d be coming in cold.
Also UCSD accepts just a handful of bioengineering transfers (42 last year) and it looks like an avg transfer GPA around 3.7 so, that’s far from a sure thing whether you are at a CC or SJSU.
If your objective was to use TAG to target a more accessible program at a less selective UC, I’d say the CC is probably the way to go.
If you were my kid, assuming those are your only options, I’d counsel you to take the bird in the hand and go to SJSU, have the 4 year experience and make the most of the campus and surrounds. You certainly can apply to transfer from there.