I was wondering what people think are the main differences between instruments which are based on a Stradivari model and those based on a Guarneri model? I'm particularly interested in sound/tone/timbre and also in differences to the 'feel' of the instrument and how it plays - but there may well be other differences which I haven't thought of.

I'm thinking particularly of new violins, but this may well be relevant to other instruments as well.

Thanks.

They have different shaped F-holes. Not that that's particularly helpful, but it's how the luthier knew that my strad copy was actually a guaneri copy with the wrong label.

Very basically, Strad models feel bigger and have a slightly brighter sound which is louder under the ear and sometimes projects slightly better (if it's not a great instrument). The shape of a Guarneri can be slightly easier to handle, which is why smaller players often prefer them, and generally have a sound that blends well in an orchestra or chamber group, but perhaps are less effective in solo situations due to a lack of power.

Genuine Strads and Del Gesus cannot be so easily categorised though, in my experience. Strad copies are often more similar to Guadagninis (known for a slightly brash sound that carries like you wouldn't believe).

The usual generalisation is that Strads speak more easily and have a brighter tone, whereas del Gesus are darker, require you to dig into the string more, but have greater reserves of power (they don't "bottom out" as easily as a Strad when you play very hard).
There are however, several instruments by both makers that don't conform to this stereotype at all. In particular, you have to bear in mind that Strad went through several periods in his incredibly long career, and instruments from different periods have very different characteristics. Del Gesu made relatively few instruments, but his style was erratic and often wild, again rendering generalisations difficult.

Regarding Strad and del Gesu models from new makers, I think it's very difficult to categorise. As bohemian says, del Gesu models are a bit more compact, but I think the sound/feel can have more to do with who made the violin rather than which model they used. Aesthetically, it's much easier to pull off a respectable looking Strad copy than a Del Gesu. There are dozens of makers in the UK who can make a nice looking Strad model, but only a handful that can make a convincing del Gesu copy (in my opinion).

If you're asking because you're thinking of buying, I would strongly recommend that you try out different models without being burdened by pre-conceptions.

That's funny because having played instruments by both makers I found the exact opposite (except your tone comment) - the Strads require a heavier bow stroke but speak to their full potential easily once you've got the hang of the bowing required, whereas the Guarneris I tried have all sung beautifully when using a less heavy bow stroke with a lot of "release", but try pushing them too hard and it's very easy to force.

Which is exactly why one shouldn't pay much attention to generalisations! It's fantastic that at your age you seem to have had the opportunity to play several great instruments. Friends in high places?
By the way, are you sure the Guarneri violins you played were del Gesus? Instruments by the other members of the Guarneri family are very different.

Some in high places, more with convenient friends...and one selling a Strad, which is how I've tried so many.
I've played 2 Del Gesus and a couple of other Guarneris. I think (all within a short space of time so it gets a little confusing). I did get to keep a Pietro Guarneri for a couple of weeks which was easily the nicest instrument I've ever played. I want it backkkkk