I've tried both synergy and share mouse and both had issues, now I use a Iogear KVM switch, it is incredibly efficient.
synergy is open source, so free, you get what you pay for IMO. But it is free so no arm in trying it out.
Share mouse, you pay per computer so it can be pretty expensive if you have more than 2 computer.
With a kvm switch, you share a mouse, keyboard and monitor. If you want you can share audio input-output, usb port. The one I use does that, very useful