The LATE 44 with phonos and chocolate coloured buttons was a good preamp, the earlier version inclined to be a bit too dry in sound with little in the way of reverb reproduction in my experience.
As for the 405, these need regular supply cap checks as the originals, and possibly most replacements, will only last ten to twelve years before leaking - I had two 405's with this problem and saw many more. As older ones are over thirty years old, you'll need to be careful. Fortunately, replacements are easy to obtain and re-manufactured boards can be got from Quad, as well as Dada Electronics. The latter supplier I've used and trust.
The older 33/303 can be transformed into charming vintage items, but need plenty of work, especially the 33, which CAN be fully updated I found. In stock form, the sonics can be variable depending on the condition of the individual units, ranging from "nice" to rough as a badgers backside. All stock 33/303's can sound tight-a*sed with iffy bass, but once the restoration starts, this bass quality can be removed and replaced with something more "expressive" and up to date. the cap coupling to the speakers remains, however.
My feelings towards the 34/306 are largely negative sadly. The former will need some possibly leaky caps looking at, the input impedance needs to be raised (the little resistor "flags" on the tape circuit) and the output level correspondingly raised. I heard one such modified and it was far better on digital sources, although limited in maximum output. As for the 306, IMO it's hopeless on percussive music, sounding flat and rather limp-wristed when compared to the others.
Hope this helps - just my impressions of course and others with different setups and musical tastes may feel different.
Buying old gear can be fraught with problems, as 1970's stuff is now pushing 40 years old. Solid state gear made in the UK back then didn't seem to have the longevity of certain components as the comparable far eastern products did and even these are starting to need attention now.
Tear down these walls; Cut the ties that held me
Crying out at the top of my voice; Tell me now if you can hear me