General Tijuana logistics
Train only runs 2 or 3 trips per day, costs more and takes longer, sometimes late. It stops at the depot in downtown SD and you have to take the trolley to the border.
Buses run about every hour from 6 AM to 10 PM from LA straight to San Ysidro. Besides Greyhound there are other discount bus lines on the same route. Google them.
Car is the quickest and more flexible with time going and returning. Traffic is tame, just be careful with pot holes and high curbs that can really damage your car. With SENTRI cars can cross back within 10-15 minutes, without SENTRI the car line is 2 to 3 hours wait every night.