So after attempting an E4 trial run and getting my butt raped because my levels are too low, where should I train? My Pokemon are level 45ish.
I used the floor with the Floatzel in Victory road. The idea of hammering the earlier e4 members is a good one, since you no longer lose half your money in DPPt.
Heart Gold has Latias
Full list of version-exclusives: http://bulbapedia.bulbagarden.net/wiki/HGSS#Pok.C3.A9mon
Of particular note is only SoulSilver has Skarmory. Then again, you can just GTS for it easily enough.