Set pieces for 4, and then something crafted for the fifth. As Niley stated, the warlock tier 9 robe is pretty bad, so get a robe made.

Also for the druid, you DEFINITELY want that four piece. Heck you probably don't want to replace that four piece until you're ready to put on four pieces of tier 10, and even then it's still being debated as to whether or not in it's current state, tier 10 4 piece is better than the tier 9 4 piece (which is balls amazing) for druids.

Short bit: Get 4 piece tier 9. For the fifth piece, buy a piece of tier 10 with your frost badges or make something. The bonus to dps (and healing on the druid) will offset the slight increase in stats you would have gotten from the off-pieces