Cisco Pix 501 VS SonicWall TZ 150

Hi,

I was thinking about getting a firewall for my network. It seems the
SonicWall is a little bit cheaper. Which one do you guys recommend over
the other and why?

Two more questions:

I can operate either of these without buying any kind of yearly service
contract right? Those are just extra filtering options and such?

Also, once I purchase a hardware firewall for the network, do you still
recommend a software firewall to be turned on, or is it then safe to
disable the software firewall?

Thanks for your expertise.