MSE is pretty good. Just remember that no AV can really prevent infections. They are more of a band-aid than anything else. If you surf the Internet with a healthy sense of paranoia you can avoid most problems yourself.
Firewall and AV are two different things. Firewall is designed to filter network traffic whereas AV is designed to detect malware and eliminate it as well as prevent it from damaging your computer.
In regard to MSE, I definitely recommend it, it's very good, efficient, and best of all, free. If you meant to refer to Comodo's AV, then I would say it's not all that good and in my experience, not all that resource efficient either.
My Computer
OS
Windows 7 Ultimate x64 SP1
CPU
Intel Core i3 530 2.93 Ghz Clarkdale
Motherboard
ASRock P55 PRO/USB3 LGA 1156
Memory
4 GB OCZ DDR3 1600 (PC12800) Low Voltage Desktop Memory
Graphics Card(s)
Nvidia GeForce GTX 550 Ti with 1 GB of RAM
Sound Card
Realtek HD ALC892
Monitor(s) Displays
20'' eMachines E202HDbmd Glare Panel Widescreen
Screen Resolution
1600 x 900
Hard Drives
Western Digital 1 TB Caviar Black Edition (7200 RPM) SATA
Hitachi Deskstar 500 GB (7200 RPM) SATA
Samsung SpinPoint 400 GB (7200 RPM) SATA
PSU
Rosewill Xtreme Series RX750-D-B ATX12V v2.2 & EPS12V (750W)
As for firewall protection, the first thing you want to configure is your router's firewall. After that the Windows firewall works fine. You can tighten up the firewall rules for the Windows firewall if you want, but your router should provide plenty of protection.