Bal and single ended, prefer balanced.If running balanced, you have the opportunity to eliminate interconnect cable interaction with your system, which otherwise can lead to expensive interconnect cables to get the system to sound right.
The only thing is, with balanced lines there is a standard which must be supported to allow this to happen. Most high end audio preamps that are balanced do not support the standard, which is also known as AES48. When looking into balanced preamps its a good idea to ask if the preamp supports this standard; if not you may find that single-end sounds just as good. But if the preamp does support the standard, there won't be any going back to single-ended.