North America is the shard we restock most often, and it is the one most buyers land on. Queue times in solo/duo hold up at almost any hour, which matters more than people expect when you are grinding placements on a second account — a smurf you can only play at 2am is a smurf you stop playing. Every NA account here sits at level 30 with the ranked queue already unlocked at the account level.
The choice on NA usually comes down to whether you want to play ten normals first. Unranked Smurf and Blue Essence Rich both arrive with untouched MMR, so your placement games are judged on how you actually play rather than on a history somebody else built. Ranked Ready skips those ten games but inherits whatever winrate it earned getting there. If you care about where you land, take the fresh MMR.