Easy to spell, high value name with excellent connotations ("supreme" as an adjective means "very great or the greatest").
The word "supremer" contains eight characters and three syllables. Established brands using three syllable names include Mastercard, Toshiba and Nescafé.
Supremer.com is a dot-com domain. Dot com is the most valued domain extension. A dot-com is the first thing people think of when they think of a website.