Guineas are great for getting rid of bugs such as ticks, so if you have a lot of ticks normally I would highly suggest getting some guineas.
But, as you should remember, they are noisy creatures. I have never met a guinea that wasn't almost always making some sort of noise.. So be prepared to deal with LOTS of noise.
Also, in my experience they are not very good mothers. This is the first year that I haven't taken away their babies. Normally if I don't take away their babies they all get eaten by something. But this year the WHOLE flock is looking over the keets. It's working pretty good too, because I wasn't even able to get close enough to grab 'em.