We considered getting guineas because of our plague-like grasshopper problem (reminds me of the bible story about Moses in Egypt!) Here's what I learned:
1) Guineas are known to be better if you have a garden. Chickens will eat gardens plants and scratch the ground until they pull your plants up! Guineas stick to weeds, seeds, and bugs.
2) If you don't teach you guineas at an early age where home is, they will free-range into the horizon. Keep them pinned up in a chicken coop/barn/shelter while they are teenagers and they will know where to come back to roost each night.
3) Our current guineas and those we have had in the past seem to make noise all day long! I see that this conflicts with previous posts. I'm just saying what our experience has been. I have three right now. Only one seems to make noise right now, but he does it all the time and it echos in the shelter! We live on 16 acres and our neighbors are very agreeable, otherwise I would definitely think we have problems.
4) To quote a guy from the Nutrena chicken workshop "Guineas will never be your best friend." I did my best to pick them up and pet them often from a young age, but every time I did they ran like I was some sort of predator after them! They struggled in my hand. They even run from me now (almost 3 months old) when I bring them food. Who runs away when they know food is coming!
Chickens, depending on the breed, can be quite cuddly. Mine almost tackle me when they know food is coming! And if I sit down in the grass, they come to join me, and a couple of them will sit on my lap.
Sorry to seem so negative about guineas...they are the best if you want to keep your garden safe! I have a fence around my garden to keep the chickens out.
Hope this helps!
Penny