To be clear, caps (or any components) with one lead coming from each end is Axial, a component with leads both coming from the same end is Radial.

Regarding capacitors in guitar amps in general: some caps will have a more pure “hifi” quality, tantalum and silver mica caps are examples. Some caps have a brighter quality (like orange drops) and some inexpensive import caps have an “out of tune” quality when used as filter caps. The common Taiwanese Illinois capacitors that Fender often uses are said to have this quality and yet there are many great sounding amps that use them. Matching the optimal cap (or any component) to a part of the circuit would be ideal and some of the best amp designer/builders are reported to have done just that. Super amp designers like Ken Fisher, H. Alexander Dumble, Mark Sampson, and others are said to have spent much time and energy “tuning” components for a specific circuit.

It’s important to remember that even a great sounding “clean” guitar amp colors the tone. If you ever tried playing guitar through a high quality hifi system you know how sterile and cold sounding a more linear amp can sound. I’ve heard that some caps can make a noticeable difference, for example an orange drop and a Mallory 150 sound different. On the other hand, I can’t really hear a difference between Mallory 150s and the more prestigious Sozo caps. Tantalum and silver mica caps are quiet but a cheap ceramic disk capacitor can bring more life to a distortion circuit (as in an effects pedal). As Andy said at the beginning of this thread, choosing the right cap is part of the fun.