oil filled or gas filled shock absorbers?

[lipoyl]

Hi all
I am in the process of removing the back numbing lowered road springs from the Bongo and replacing with some practically new ebay bought standard ride height originals and I think its probably a good time to replace the shock absorbers at the same time. I was going to buy the normal genuine Mazda Bongo oil-filled shock absorbers but then ava asked if I wanted the gas-filled ones (obviously not original) as these are the modern "higher spec" versions. I have a 1996 auto 4x4 with 110K on clock auto free top model - so my question is should I stick with the original mazda oil filled shocks or is it an upgrade to go for the gas filled ones, incidentally at same cost. I don't want the ride to be harder than that acheived with oil filled ones but aim to get the most comfortable ride i can get.
many thanks for your time

Paul