Best type? Whew. I don't know if I can answer "best". I was running DonChamp. I was owned by a psychic deck (lost zone is brutal when you run stage 2s). Yanmega was in loads of decks (mixes of magnazone or donphan a lot) and I saw lots of fire. Yanmega kept shooting over my head and taking out the bench. I never played against a single VilePlume which is great - I was dreading that. ReshiPlosion and ReshiBoar everywhere (and once they get set up it is a non-stop hit for 120 every single turn - brutal). I think I saw one dark that went into the PC top cut, but I didn't make it in so I don't know what it was or what made the cut in general. I think that most folks ran pretty much what they ran in Nats (I did too). I was going to watch PC top cut, but I went to watch the final 3 games of regular play with my kids to see what won Nats (not that anyone could actually see - please guys, video is our friend).
Anyway, fire and grass seemed to be everywhere and very effective - Nats and Professor Cup both. I was very pleased to see that fighting won nationals - sort of - as it came down to whose Tyrogue woke up first. It verified my decision to include him and choose him as my starter in PC. Of course I ran Machoke - who knocks out sleeping babies (is it just me or does that just sound wrong? <grin>).
Not sure if I answered your second question or not, and I would love to know the answer to the first one myself.