Nobody from Bitdefender partners use a older engine. They can all use the exact same engine as bd. just some delay on the sync servers. thats why bd often have better detections/signatures than the other ones who use bd engine.Avira, cloud protection, good detection and you can use the free version and it is ok
Bullguard = old BitDefender engine, and BitDefender has some FP and you will see a delay between BitDefender and Bullguard detection so in a real infection that in not good.
I use Avira Free + WinPatrol, I feel happy with this setup.