Well mate, if you know the fella breeding them and you know they work and can find and stay well, and if you like their style of working why go for anything else ? You'll have a better chance of getting yourself a worker off dogs you know are proven,
It's just my thoughts on things for what it's worth. and in the end unless you specifically like the look of a certain type, does it really matter what they look like if they do what you want of them.
Some of my best workers have been Russell crosses tho
All the best