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Because they've spent a "life" under load and in a particular shape, I'd anneal them at least a couple times before doing any forging. Then flatten them, normalize, and see if they still have a memory. You want to get rid of that first.
The other risk is cracks - small little ones you can't see at first, but might show up during your heat treat. That's just part of the territory with recycled steel - and it all depends on how the spring was used during its life as a spring.
Your question points at my third priority, which is alloy - that will determine how you heat treat, if you're really trying to get all you can out of the steel. Some are better than others, yes, but if you're getting seconds as a major source of steel, you'll have to adapt to sub-optimal material and develop a HT routine that'll make a decent knife without knowing the exact content of your steel. Usually that means a gentle oil quench and 2 hour temper in the 300-350 F range. Less rockwell points, but good solid knife material that can be had in droves if you get a good donor.
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Hammer on!
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