Given the choice between the two, XLR wins hands down for fixed (back-of-the-rack) interconnect.
XLRs offer three big advantages over 1/4" TRS connectors. First, the connector itself offers much greater contact area between the male and female pins. This offers greater reliability over the long term, and reduces the chance of crunches, distortion, or signal loss due to oxide in the contact area. 1/4" TRS plugs have very small contact areas between the spring fingers in the jack and the T and R portions of the plug by comparison. Second, they latch in place: always important, even if you think the rack will never get shaken... and third, they do make the ground connection before either of the signal connection at a mate cycle, and break ground last at a demate cycle, not that that matters much for fixed use.
For patchbays (as opposed to fixed interconnect), the only advantages that 1/4" TRS connectors offer is density (and bantams are even better) and long-term *multicycle* reliability (if and only if you buy the expensive telephone-style longframe hardware).
I always use XLRs whenever I can: the chassis mount XLR connectors are vastly more reliable than the cheezo plastic shortframe 1/4" TRS jacks used on most equipment these days.
Time for another skippy story. One other thing that's a habit left over from my misspent youth: I always use Cramolin on all fixed back-of-the-rack interconnect. I'm told that that product has been discontinued, and DeOxit is now the hot setup. Could be... Anyway, I have about a quart of each of the parts (it's a two-part goop)left over from the old studio, and to this very day I religiously clean/deoxidize the plug and jack, and put on a coat of the preservative, before I mate the connector- *especially* if I have no plan to ever touch it again. This is actually pretty important for the fixed interconnect, especially if you use any vintage gear, and *especially* for 1/4" TRS jacks with that tiny contact area. If the environment is anything less than pristine, rot can set in, and after a few years the crunches start. And I _hate_ trying to find a crunch when the talent is in the room, tuned up, and ready to play.
Before you guys rag on me about using an "audiophile product", hear me out. The stuff does make for a somewhat more reliable connection in the long haul, and I have conclusively (and painfully!) proven that to myself in the field. When I was still back in Boston in the late 70s and early 80s, my band did a great many booze cruises: on-deck gigs on cruise boats out in Boston Harbor, basically a floating frat party. If you have any weather at all, you have salt spray coming over the rails- and you gotta believe me when I tell you that the connectors go through _hell_. I had one PA rack where the XLR connectors to the power amps corroded in place, and the entire connector had to be replaced when it came time to change the rig at the end of the summer season. You coudn't have demated those connectors with a freakin' tube-maul.
I was introduced to Cramolin in our second season of booze cruises when we couldn't get a clean signal out of the guitarist's old Bassman 50 for love or money- the corrosion on the connectors was just disgusting. One of the frat-boy attendees on the boat suggested I try the stuff (between heaves over the side, as I recall). What the heck, why not? Back on shore, I found a place to buy some, used it, completely restored it to function, and started going through the whole rig. The crunchies went away, never came back, and I just never have stopped. Shoot, I even Cramolin tube socket pins: that once solved an intermittent crunch in one of the other amps. Once I find something that *works*, I tend to stay with it...
Do you need to do this? Probably not, unless you have salt spray in your room (or live in a coastal area, or one with really high humidity)... Just the same, I claim that a few extra hours of upfront work can yield years more trouble-free operation. This one is my religion, even though it might seem like turd-polishing to many folks. You'll get no argument from me on that topic: I've always been a belt-and-suspenders kind of guy...
