After falling prey to some scum bag and suffering a loss of my much loved
bicycle, I've decided to do some research into locks.

The bicycle had a D lock with a round key which is aparantly crap, and a
chain lock with a padlock type lock connecting it. I left the bike 3/4 mins
came back it was gone in a very busy place, I guess no one cares or people
with there busy lives just walk on by.

The advice I'm after is what kind of lock(s) would be best for me ?

I've had a bit of a knock confidence wise even buying a new bike, but I have
and just wanting to make sure it doesn't happen again. Although I know it
can if the theif wants it they will get it, I just want to create enought of
a deterrent to make them think too much hassle.