Oliver Marcus flows more easily off the tongue. One thing that I think helps names flow is to alter the syllables per name. Oliver (3 syllables) and Marcus (2). Also alternate the vowel sound... I agree that Archie Marcus has too much of an "Arrr" sound about it.
I like Oliver, but then I like more traditional names for boys. Then Aiden (reminds me of sex and the city LOL) and lastly Archie...I don't really like Archie, sorry. It's a gorgeous *boys* name, but it's not really a man's name IMO.
Bookmarks