I've been slowly replaying Platinum, and wow. What a fun little game! I just got past the third gym, and it was tough as nails, but I got through it thanks to dark type moves.
My current team consists of Prinplup, Luxio Buneary, Ponyta, Eevee and Bidoof (I think Bidoof will be replaced with Ralts... but I have him there for not just for HMs).
You should replay Platinum!