I've been to Baguio several times already using my suzuki van. F6A engine 12-valve. In my experience, I spend more on my gas going up to Baguio than in going down and travelling back to Manila. The maximum number of passengers I accommodated is around 3 (adults & me included). This does not include the amount of baggage and personal belongings my passengers brought with them.
As a practice, I ask my family to pack light. It's easier going down from Baguio on a full load rather than climbing up.
I have already taken the van up on both sides (Marcos H-way and Kenon). The van is quite reliable and I guess the big problem one really has is traversing the NLEX. Buses can be a pain if you are carrying light load. The van slightly sways with the wind drag caused by the passing buses. However, it's not really a problem if you are used to this.
I have 3 stop-overs on route to Baguio. The first stop is the Gas station on the first leg of NLEX. My second stop is in Luisita Mall and my third stop is in the Victory Liner stopover just before going up to Bagio.
It's a fun ride if you enjoy the driving rather than getting peeved by the numerous assholes wanting to overtake and speed off like some crazed bat out of hell. Just let them be, they will die soon enough. hahahah... (joke).
The best driving experience can be had if you go up to baguio at a very early time. (3-4 AM). For me this works well. Considering the amount of time my family mills around at every stopover, it's really a good time to go too. You will arrive in baguio earlier and you wont be inconvenienced by the traffic at every provincial capital. You will at least get to baguio nice and fresh. (I really hate the sun.