I would not try unless you have scores that are 650+. With 700+ being preferred. But remember, your score is not the only factor. Citi (and most creditors) will also take into account your payment history, mix of credit, DTI, collections, ect.
I have heard the Citi Diamond Platinum Select is the easiest to get.. Not sure how much truth there is to that.
Also, Citi is a big EQ puller. Assuming you are approved with a low CL... do not fret! Citi is VERY generous with CLIs for responsible card holders.