My 2 cents (very close to what SpectriaForce said) :
For Sound Cards - Polymer caps might sound a lot worse, and are usually not recommended for sound. Electrolytics are usually the way to go. And a good all-around cap is the "Panasonic FC- series".
For motherboards and anything else, you have to be very mindful of the specific task each cap is doing.
For high performance stuff like around the CPU, you need to have top-of-the-line caps with low ESR, for example.. You can't go replacing all caps with just one model for everything, unless you have a lot of money to spend on THE BEST model.. (and that can also backfire in some situations, where high ESR is actually part of the design)
So if you want to do this smart, there's kind of a lot of work involved in getting to know WHAT caps are on that board in order to find a proper polymer replacement.
My advice is, don't bother unless it's broken or it's acting strange.
And also Electrolytics aren't all that bad, if you buy good quality ones. Panasonic FM-series for example have very low ESR, and should last you at least 20 years if they're not overheated. Just an FYI.
Also, as a rule, you could also go with higher voltage caps to get better ESR. Only side effect is that the higher the voltage, the bigger the cap's physical size.
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For testing caps & ESR, i strongly recommend you at least get "The TransistorTester". It's a relatively cheap device usually found on AliExpress or Banggood, based on an open source project, that (among others) measures capacitance, voltage drop, & ESR quite accurately! It has many forms and revisions, so do a little research first.
Just be sure to ALWAYS discharge EVERY cap before testing it... And don't test caps that are soldered in a circuit.