safety/security tool HELP!!!

Viruses and worms
1

HI on sunday 21feb was subject to the above fake av virus. after alot of effort manged to delete fake prog then updated my avast to avast 5.0 and did full scan. it found win32:trojan-gen 36185528.exe which if removed so far so good i thougt lol.came back to pc few hours lata and avast said real time prot off i turn back on shut down pc. rebooted following day avast would not lunch error said side by side config changed or corrupt. down load microsoft security essentials then unistalled avast while i looked into this.did 3 full scans nothing found. looked on here down load mbam did full scan it found 252 infections 247 adware 5 trojan agents!!! ques is why did avast & microsoft find then as some must have been on pc for sometime used avast for last 10months and next ques is it worth continuing with security essentials or avast or is it wise to purchase something like norton mccafee etc any advice is most welcome as my brain is now in melt down

2
is it worth continuing with security essentials or avast or is it wise to purchase something like norton mccafee etc any advice is most welcome as my brain is now in melt down
Avast free + Malwarebytes PRO (protection modul with IP block and autoupdate) a one time fee for a liftime license
3

THANKS pondus i have a 1yr subscription to norton which i havent used yet is it worth it and any idea why avast & microsoft didnt pick up on the adware infections( have to be honest avast4.8 did pick up 9 viruses in the time i used it) im not to sure about security essentials. also task manager keeps coming up as corrupt or tampered with have followed microsoft instructins to reset but when i click on polices nothing happens!

4

No security program have 100% detection, if they did there would not be a virusproblem
Tomorrow avast will detect something Norton and McAfee dont detect.....and the next day...... You just dont know what program that will detect the next bug you meet…
When it comes to detecting bad websites avast is probably the best in the world…
and if you then also have MBAM with IP block