don't even think of running two scanners
the rule is
1 virus
1 firewall
and as many malware scanners as you can eat
(I think most people will agree with this)
the bit we all differ on is what brand to go for
and to an extent it depends on your surfing habits
bbc and ab - a free set of tools is good enough
avira and avg both do freebies
if you have a couple of quid to spend ... an all in one suite is probably your best bet
the current winner of all the mag reviews is avira
it replaced kaspersky who held top spot for 3 years (and that's probably part of why it was replaced)
both come with a 1 month trial
kaspersky will give you another 60 days if you register at
http://www.kaspersky.co.uk/safeonline
and an oem copy is a cheap way of getting it
http://www.google.co.uk/products?q=kaspersky+o em&hl=en-GB