It's difficult to vote though...
"S.O.S." is probably her second weakest lead single, "Umbrella" was the song that made her to a worldwide pop star and is still one of her signature hits. "Take A Bow" is a little bit overrated IMO, for example DSTM is much better and deserved a #1 position on the Hot 100 too. "Disturbia" is amazing, i really loved it back then. "Rude Boy" is a good pop song but i prefer "Russian Roulette" tbh... i was quit surprised when i found out this was #1 in the US... i mean the lyrics
"What's My Name" and "S&M" are both great, but by far not her best work. "Only Girl", "We Found Love" and "Diamonds" are all AMAZING lead singles... so i think i decide between these three (i won't count "Love The Way You Lie" and "Live Your Life" in because their not her singles...).
Well... i guess i vote for "Only Girl". WFL and D both will get enough votes by other members, especially the first one is too generic to be chosen as her best #1 single IMO... so yeah, OG FTW! (and i also loved her red hair and the whole look on the cover/clip!)