RCA or XLR?

Xlr all the way as it has an isolated separate ground.it has an advantage on longer runs as well. 6 more db as well. Happy hunting.maybe rca sounds better on some cuz there not truly balanced.

@opathy 

The same thought I had. I've had some RCA connectors for decades... especially when young and never had any wear on them even though I used to fiddle with them a lot. 

I hate to come across as being negative but reading through these comments is disappointing. There's so much misinformation on this topic, I don't even know where to begin. I guess you can start by forgetting about the cables. Focus on what you are connecting. That's what's important. Balanced and single ended equipment is not compatible. The reason an RCA cables are the most popular type for home audio equipment, is you only need a 2 conductor cable for single ended (non balanced) connections. For a balanced connection, you need 3 conductors. That's why XLR is used. The only way you can have a balanced connection is if the 2 components you are connecting can support a balanced connection. An XLR jack isn't good enough. It has to be balanced. If not, the connection defaults to single ended and you are only using 2 of the 3 pins on your XLR cable. And when that happens, it is an RCA cable. If both components can't accommodate that 3rd conductor in your XLR cable, it doesn't get used. I can tell by reading the comments, that this is exactly what's happening for most of you. Its the components that dictate what type of cable you should use. Not the other way around.

At this point, I know some of you are triggered. Yes, I'm oversimplifying here. There's more than one way a component can be balanced and there's more than one way to wire a balanced connection. For example, sometimes you can use an rca/xlr adaptor and it will work just fine, and sometimes you create a short circuit the second you plug the adaptor into the component. If you've ever wondered why they put pin diagrams right next to the xlr connectors on the back of your equipment, that's why. If you are not sure what to do, start with your owners manual. If you have a mix of xlr and rca connectors on the component, the manual should tell you what you need to know. If not, call the manufacturer. Even if you can use an XLR cable with no issues, why buy one if you don't have a balanced connection? Balanced cables are more expensive because of the extra materials it takes to make them.      

Balanced differential, XLR, cables don’t necessarily sound better than single ended cables but they do remove any noise, electromagnectic, picked up along the signal path in transmission.  That is their main advantage.  Metallurgy, impedance, capacitance impacts from the insulation, can affect both XLR and single ended cables.

I use XLR - smart people at Boulder do not include RCA inputs on their equipment. So even with my not fully balanced phono stage I use XLRs. No complaints. 
Oh and to add - XLR and RCA ins/outs have different gain and impedance when it comes to fully balanced gear. So when you’re comparing XLR to RCA even using same cables, take this into account. It’s all about matching. 
So use whatever you feel sounds best.