I still agree with Jinx, but I dont personally like the argument that "yes canon, but they wouldnt do all of this."
We should consider counting that point in the argument, no matter how strong or weak it is.
A better argument would be imo "yes she can freeze her, but her blink can jump her back out of freezing range."
As a rationalist, I believe a strong argument is when you can have multiple points and you can work with countering as much as possible.
If you want full blown analysis of someone who loves both characters, stay tuned.
Long range combat
Ruby easily. Ruby's rounds are good for hundreds of feet and have no damage drop off. Ruby does not like to use long range combat, but she has been shown to be capable of doing it with some grimm (I forgot the name of it, but start of season four.)
Medium Range Combat
Still Ruby. Even at this point at ten or so feet, Ruby has the range advantage and is probably what she is best at (besides close range, but I will get to why tracer stomps close range). Ruby has the better range with her scythe and is probably more more lethal if she does get a hit in. Tracer is really fragile, both in game and out of it and is not accustomed to taking hits. She also not used to using rewind, I have only seen it at best twice in canon, once in her fight with widowmaker and I think she used it once in a comic (and dont even quote me on that). Using the cinematic, the pulse bomb does even it out since she can throw it for ten or so feet. She is stuck and blown up, if it does scale, then it is game over. (which to be honest, I guess so. I want to give this to jinx on the sole grounds that it would be ridiculous to assume that it is weaker then her normal weaponry)
Short Range Combat
Tracer. Tracer is very good at kiting around opponents like Doomfist, Widowmaker, Reaper etc. She is the best kiter/flanker in overwatch and to be frank, if it ever gets to this pont, I dont see Ruby winning. Her blinks is relatively instant. Now, it isnt unfallible. She is somewhat predictable, taunting her opponent so much so
Doomfist still predicted her combat patter. I still want to give this to tracer, she is so over confidant that it is in character for her to just taunt her opponent for a bit, but at the same time, Ruby isn't the greatest at predicing combat patterns.
If it was Weiss or even Blake, I would lean to them because Intelligence and Experience, which ruby has neither of these things to their level. Tracer was a soldier for a few years at best, her primary training as a pilot is not indictive of her as a soldier.
Freezing
Yeah, we shouldnt make the false equviliancy to say that she can freeze to weiss levels, but she doesnt need too. Not saying Tracer's kryptonite is freezing, but she can be flashfrozen and killed easily. Immobilizing her.
Now in character would she do it? Maybe, not immediately. But considering Tracer's personality, if Ruby has any semblance (pun not intended) of being tactical, then she will figure it out.
She did figure out something was wrong during Cinder's infiltration mission and she also felt someone was wrong with the nucleave grimm (can't spell his name but whatever), so I want to say it is possible. Don't want to just dismiss it entirely.
Other:
Ruby's intangibility iirc (either Jinx or Weekly can correct me on this), only works for a second/few seconds at best. It isn't always on and it is part of her semblance. It still gives her the defensive advantage against's tracers small AP advantage (I think they are both baseline, but tracer is a tad higher).
Tracer is smarter via book smarts, but Ruby is probably more tactical just by a hair. I am using the doomfist example against her, and Ruby's creative nature with her semblance in the Red Trailer, end fights in both volume 1 and 2 etc.
Tracer has probably the more combat oriented experience with other people with a greater variety of abilities, but Ruby has more fights under her belt.
Tracer's blink is literally her entire style. The two best counters to disable it, is to freeze or keep distance from her. Ruby's scythe does give her that ability, I personally think eventually Tracer will eventually figure it out and just rush in, pulse bomb, one clip her and get out.
Speed is equal, but Ruby has the speed advantage via semblance.
Alright, to sum it fairly as someone who loves both:
Ruby's path to victory
In character, no stretch: Just spam her natural distance. Even at a few feet, Tracers rounds drop off badly. You need to be about 7 feet of distance to do max damage, which considering Tracer has to get past that scythe of the exact same distance, it will be hard to do. Even if she has blink, Ruby's scythe motions are usually either to rush an opponent or spamming her general range/360 degrees of motion. She may have the lower ap, but the intangibility difference and her speed does give her a path to victory. In the first few minutes, Ruby can spam her natural range, freeze her possibly and win. Or just keep her distance, fight with her scythe in swinging motions and just force tracer back. She can't blink towards a weapon strike.
Tracers path to victory:
In character, no stretch: Tracer is cocky, but she isnt stupidly so. Long term, she will probably find a weakness in Ruby's fighting style. I say this considering that she is naturally good at taunting her opponents to exploit weaknesses... See the Winston and Tracer vs Widow and Reaper. This turned out to be in her favor. Also, if it wasnt for venom mine in the end of widowmakers cinematic, Tracer could have won considering she had her running away because blitzing Widowmaker is easy. If she gets one pulse and one clip on her, she gets it. Aura can't protect from higher ap in most circumstances, and one pulse bomb and one falter is really all she needs. Instablink to her comfortable range, clip her and kite her.
Tracer takes this with high diff. Although I write this, biased as a tracer mai

. Like, She literally has thrice the number of wins then most of my other heroes.