I'm not brand-loyal to either of the brands you mentioned, nor in fact to any brand, though I'm happy with the performance I'm getting from my current brand of choice. If a better camera for my needs were to be made by another brand, I'd have no problem switching, even despite 5-figures invested into my current brand...if I am not happy with what I've got and something else can make me happier, I'd switch. Fortunately, no need to at the moment.
That said - you really might not need to consider a brand switch at this point. The overall performance between Canon, Nikon, Sony, Pentax, and non-DSLR competitors from Sony, Fuji, Olympus, and Panasonic are all so close that only more extreme photographers will ever be pushing the cameras to those performance levels where differences stand out...average hobby photographers will likely never really notice the differences between brands in most normal shooting. Nearly all sensors out there are being made by the same manufacturer anyway (Sony), with the only exception being Canon...and the difference in the newest Canon sensors and newest Sony sensors again is very small, unless you're really pushing the limits.
For you, coming from a 6-year-old camera, the advances in technology and performance since then will be huge - ANY brand of camera with the same sized sensor or larger will easily and handily outperform your 6-year-old T1 sensor, and by a fairly significant margin with regards to low light performance. Based on the lenses you have, and your stated hobbyist level, it's quite probable that you don't really need to step up to a very expensive, very heavy full-frame body and the requisite better lenses needed - modern APS-C cameras will be significantly better than your current camera in every regard...more resolution, sharper, better high ISO performance, faster and better focus and tracking, smarter algorithms, and so on. So first consider whether you really want or need to step to full frame (not that there's anything wrong with it - just that it might not be something you'll really be getting the advantages out of - if you buy a full frame camera and only push it to 20% of its abilities or use it with basic kit and zoom lenses. Just something to consider.