Well, there is tons of types of springs and more importantly spring layouts. Some manofacturers will use less springs than others, and that is very important.

Personally I prefer spring mattresses over foam mattresses. They last much much longer as dangrossman commented, are more reliable and also much firmer. And also you can't leave aside the weather factor because spring mattresses are way more breathable than foam-only mattresses. We, for example, avoid selling foam-only mattresses to people that live on high humidity areas because there is a high chance they will return it with humidity stains.

Normally I would go for a pocket spring mattress ( I think that's the term in English for a mattress with individual sealed and padded springs ) with a decent amount of memory foam on the top. That way you get the firmness and breathability from a spring mattress plus the comfort of a nice soft memory foam layer.