Sister As Maid Of Honor

Is it tradition to ask the oldest sister to be the maid of honor? do people expect to see the older sister standing next to the bride? i have 2 sisters, im closer to one, but the older one will probably really have her feelings hurt if she isn`t standing next to me, and quite frankly, i want the younger one next to me. I have already decided to name them both as MOH, but choosing who will stand next to me is going to be difficult. I figure i should choose who i WANT, but was just wondering if choosing the oldest when you have multiple sisters, is tradition or something.