To each their own, and for our operation I use border collies. However, as previously mentioned, they are not as aggressive as some of the other herding breeds.
The border collie had it's origins as a sheep dog, therefore it needed to be a bit softer than breeds develop to work with cattle, but I've gotten pretty lucky. My bitches have far too much "grip" to be good sheepdogs, but they will take a bull or cow by the nose and turn them if need be. It's a toss-up as to which is the better dog, because the older one is more aggressive but also very "sticky" and therefore needs to be kept on track more frequently (to my agenda - not hers), but the younger one, although somewhat less confident than her aunt looks back more often for direction, which I prefer rather than trying to untrack the sticky dog.
Neither can be trusted loose unsupervised, as they will work whatever stock is handy, be it horses, cattle or chickens (favourite chew toy of collies on my place...must be the fun squeaking sound they make when feathers are pulled out of them.). But if you need to move a unco-operative animal into the sorting corral or onto a liner, they're worth their weight in gold. I've seen them catch an occasional hoof in the chops, and they just get right back in there and work that animal over. Also mighty handy for keeping the cows out of the hay yard gates when it's choring time.
Oh, and they're hell on bears and coyotes. They'll tree a black bear at the drop of a hat. I also haven't seen a wolf close to the house since I got them (not to say they haven't been by, just haven't seen 'em). On the downside, if left to their own devices, border collies and most other herding dogs can develop a fatal attraction to vehicles.
It's kind of interesting to see what kind of dog everyone prefers and why. Basically, do some research on the different breeds and it's really worthwhile if you can get in touch with someone who uses/trains/trials stockdogs. It'll let you get the measure of what you think might work for you in your situation.
Take care.