I used to use Qihoo happily until I began finding things such as Windows Updates being blocked because of the Proactive Defence. I suggest if you are a user, go check the logs and see if anything has been blocked (by default, anything over 30 days old will have been purged from the records). Of course, 360 has a good cloud, and very nice heuristics, but if you have no connection then you only have offline databases which are probably over 12 hours old. So even though I could disable the Proactive Defence, still it isn't good enough for my taste. This is not to mention another, perhaps more serious problem which is that the Proactive Defence executable file is always busy, no mater what settings it has.
Baidu isn't good enough either. It's obvious that they're serious about their antivirus, because they've clearly invested a lot of money in it. But the problem is you simply don't see this investment resulting in fixes for old problems like the very slow Avira database updates, for example. It seems that the actual antivirus functions are not their main concern with this product.
avast! is a solid free option. Bitdefender may be a good free set-and-forget option. Both are good paid choices. Norton, ESET and Kaspersky would probably be better, though, although using the 30-day trial versions and analysing details of each program would be ideal for you to make a choice. Webroot was buggy when I tested it, didn't like it much anyway, so I don't recommend it.
I'm using Lavasoft Ad-Aware Free, for me the best Bitdefender-based choice in free editions. Stable, good interface, database updates are on par with Bitdefender, no additional components are installed if they are not used, does not nag you (only asks if you'd like to recommend it in social media after cleaning infections, nothing obtrusive).
For extra heuristics, I use Kompas AV as a companion.
Also you may not need an Internet Security package, sometimes a simple AV with Windows Firewall is enough. Sometimes less is more, fewer programs equal more stability, and sometimes even more safety.