My bet is on cylons. No matter how much passionate warriors the klingons are, the cylons have superior technology and will just nuke the klingon empire. That would actually be a GOOD DAY TO DIE!! Qapla!!!!
Now you realize... the Klingon's technology is technically superior to the mass driver-based weapons and technology of the Cylons, right? The one thing Cylons have against the Klingons is the swarm-mentality where they have a hive ship and swarms of fighters.