What is your price range/use for them? The cheaper pair I have are the Wahl Pro Series (which come in cool colors
). They're great for the price. I've had them for years. They're perfect for the occasional light clipping: whiskers, ears, fetlocks, and bridlepaths. Lightweight and easy to handle. They're not particularly powerful but they do get the job done, esp if you only have a horse or two. The pair I love are Oster Power Pro Ultras. Much more expensive but very powerful, very fast, quiet, etc. They making trimming a breeze and strong enough to body clip. The battery lasts a lot time but they give you a 2nd just in case it runs out while you're using it.
One of my friends bought a pair of Wahl Arco's and they were horrible. They only lasted a few months and she had to get another pair. I think in general though Wahl and Oster tend to be good brands.