I'd recommend G rank Tetsu and then G Rank Seregios shortly after; you'll then be set till end game armors then.
Both of those are monsters I'm quite comfortable with fighting.
Another fun suit I've been rocking lately near the end of high rank is Black Gravios. I had a group of people all wanting to clear HR 5 and after fighting it only three times had all the pieces. Tons of slots, tons of defense, healthy fire resistance, looks like a boss. Just wish I was a lancer but the few times I've blocked with my great sword I've really noticed the effect.