Until recently we had 2 Great Danes, one Bullmastiff and one English Mastiff, sadly we lost the danes, not long lived dogs unfortunately, and have 2 Saluki/whippet Lurchers as replacements for them, both from rescue kennels.
They have put a new lease of life into the two Big Boys, and are excellent rabbit catchers.
The Bullmastiff is very placid most of the time, but hates Border Collies and Black Labs, the Mastiff is very timid, and does not like being the focus of attention, so will hide in bushes when he feels intimidated.
The two Lurchers are very friendly, but one likes to play "rough" and can be a bit over the top at times, so has to be watched quite closely at the moment, but we have only had these 2 dogs for 3 months, so they are still settling down and testing the limits of acceptance.