It's probably safe to assume they have enough miles on them that the ride would benefit from new replacements. So starting there, you could replace just the front struts and get a much improved ride out of it. Adding in rear shocks to that would be best but not absolutely necessary. Replacing all 4 shocks and struts would yield the best improvement in ride quality obviously.

As far as performance upgrades go, you can get some benefit from going with the performance versions of whatever shocks/struts you buy, but it won't be a lot. In order to get a true performance suspension feel, you would need to also replace the coil springs and anti-sway bars too. Replacing the springs with some SRT springs would yield an improved suspension akin to a performance upgrade, but it will also lower the car an inch or so. So that should be kept in mind.

Also, you could do the strut assemblies, shocks, and coil springs with performance alternatives and not do the anti-sway bars, but it would be best to include them. The main reason to not include them would be the labor involved to replace them. The front anti-sway bar isn't terrible to replace, but the rear one requires dropping the entire cradle, which can be a pain if you're doing it in your garage with only jack stands and a floor jack at your disposal.