Formal in what context? Business formal? Black tie dinner formal? Which country/culture?
The most important things (for shoes, but also for other clothing) are-
1) Clean (this means starting the day clean, as mud etc acquired during the day because of adverse conditions shouldn't be a problem).
2) In good repair (which doesn't have to mean new, but does mean looked-after).
3) Comfortable - you may not be able to concentrate/do your best if you are uncomfortable.
For women, pumps would generally be considered business formal, unless perhaps the pumps have very high heels (which might put them into a different category of business attire).
Suede is generally not as hard-wearing as polished leather and can be more difficult to clean, so is less practical for day to day wear in a business context. But that doesn't mean it would not be considered formal wear for women. For men, there is still the possibility that suede might be seen as "country/informal".
