Connie, reasonably comfortably. I'd estimate a significant advantage in shields, sensors, speed and agility for the Connie, and maybe an edge in firepower for the D7.
I'd also rate the average Federation Captain probably better than the average Klingon captain, though that's just an impression.
I wouldn't say the advantage is overwhelming, though. A really crackerjack Klingon commander could well have the tools and talent to take a merely average Connie apart.
Give a man a fire, and you keep him warm for a day. SET a man on fire, and you will keep him warm for the rest of his life...