If the train goes exactly where you want to go, I would always say take the train. It's spacious and clean.
But if where you're going is only served by bus or requires some walking... it really depends on how you feel. Waymo is pretty expensive, but I have had some truly miserable bus rides in SF.
There is a reason I picked the 49 as my example. When I lived there 15 years ago, the busses were lacking to say the least. Extremely slow, got stuck in traffic, crowded, etc.
Since the BRT lane on Van Ness, taking the 49 is more like taking a more shaky Muni train honestly. Frequent enough that it doesn’t get crowded, and it doesn’t get stuck in traffic, meaning much faster ride. As San Francisco builds more of these bus lanes, the case for the robo-taxis is only going to get weaker.
But if where you're going is only served by bus or requires some walking... it really depends on how you feel. Waymo is pretty expensive, but I have had some truly miserable bus rides in SF.