I have mules, jacobs, southdowns, dorset downs, risingtons, suffolks, romneys, lleyns and finally a couple of portlands that I got becuase I wanted the dog that came with them!
I find the lleyns the easiest sheep to manage from lambing to shearing and worming etc. My husband demands we keep some dorsets as he says they taste the best and the other sheep we had to make up the numbers and to ensure our dogs get to meet allsorts of breeds of sheep.
The only ones I dislike and I mean really dislike - are the portlands; they are small sheep and therefore easy to handle - if you can catch them! The breed are kept with long tails which can get manky in the summer and they only ever have one lamb at a time - plus they don't flock they scatter!
As for horned with non horned - I think the only regulations are that they should not travel together but I might be talking about cattle! I have 150 ewes of all the breeds and they are all in together.