I'd stay away from Rottweilers if I were you,
@exia
I once got inspected and 'herded' by a Rottweiler and German shepherd when out for an early morning cycle. The Rottweiler merely rubbed his tooth against my lower leg and that left a wopping dark bruise about the length of my thumb. I was on a rural road and man was I frightened. Just at that moment the farmer came round the corner of his building and called his dogs. I had not been on their property.
Anyway, rottweilers are not any smaller than labs. We had a lab when I was growing up and she wasn't a problem with the guinea pigs. We even had them in an open-topped cage in a room the dog was allowed in. Though from reading on here, that's maybe not the best plan, not 100% safe.
My neighbour has a lovely sweet little poodle. A bit hyper, very friendly, wants to greet everybody and be stroked. I don't know how poodles are temperament-wise with little herbivores. But obviously the breed has to appeal to you too. I think I wrote a bit about our lab and my guineas over on my thread called My guineas. If you're interested.