An extract showing different button types you can use in SPFx web part properties (from getPropertyPaneConfiguration() method).

SPFxWebPartProperty_Buttons.ts

groupFields: [
  PropertyPaneButton('', {
    text: "Normal button",
    buttonType: PropertyPaneButtonType.Normal,
    onClick: this.cobWPPropButtonClick
   }),
   PropertyPaneHorizontalRule(),
   PropertyPaneButton('', {
    text: "Primary button",
    buttonType: PropertyPaneButtonType.Primary,
    onClick: this.cobWPPropButtonClick
   }),
   PropertyPaneHorizontalRule(),
   PropertyPaneButton('btnHero', {
    text: "Hero button ('Add' icon)",
    buttonType: PropertyPaneButtonType.Hero,
    icon: 'Add',
    onClick: this.heroButtonClick,
   }),
   PropertyPaneHorizontalRule(),
   PropertyPaneButton('', {
    text: "Command button",
    buttonType: PropertyPaneButtonType.Command,
    onClick: this.cobWPPropButtonClick,
   }),
   PropertyPaneHorizontalRule(),
   PropertyPaneButton('', {
    text: "Compound button",
    buttonType: PropertyPaneButtonType.Compound,
    description: 'With some descriptive text',
    onClick: this.cobWPPropButtonClick,
   }),
   PropertyPaneHorizontalRule(),
   PropertyPaneButton('', {
    text: "Icon button ('AddFriend' icon)",
    buttonType: PropertyPaneButtonType.Icon,
    icon: 'AddFriend',
    onClick: this.cobWPPropButtonClick
   })
]