Class makes a big difference to this question.

Both races have passives that come in handy in trials. And honestly, with the CP system and gear you're going to be boosting their weaknesses, bringing them closer to one another where it makes even less of a difference. But what's our base difference?

Khajiit
20% health recovery.
Stealth buff...lower detect, more damage from stealth
8% weapon crit

Redguard
10% max stam
Melee returns 3% stam

Hum dee dum. So I'm going to call the stealth and stam regen passives a wash. They're both nice, but not game changers. On a redguard, I'd estimate you'd be getting back 1,000ish stam every five seconds. This is good, but on the other hand with a khajiit you should be attacking from stealth a lot and that buff means fewer hits to kill. If you're a nightblade, I think the khajiit slightly wins this passive compare because they stealth a lot and have siphoning attacks to offset the recovery loss. if you're a Templar I think redguard edges out slightly, although in trials I find that repentance gives me plenty of stam.

The real question is the max stam or the crit. Again, I think Templars or DKs love the max stam while NBs love the crit. For my khajiit, I boost the CPs for physical damage and crit damage, and he crits 75% of the time. In my mind, that's pulling a lot more damage than a 10% stam boost would. But 3,000 stam increases damage for every stam attack, which is good. A distinction here is that there are some ways to get crit high enough without this passive (camo hunter, for example), but finding an addl 3k+ stam is tough.

The health recovery is a big deal to me. It would cost..,what? 60-70 champion points to buy 20% health recovery? I find I can spend these on things to more than make up for the max stam or melee passive on redguard, so I've always like Khajiit.

Play style also makes a difference in this question. I stamblade a lot of trials, and in the craziness I'm often buffing and dark cloaking out of trouble and then turning around to wallop someone. For that playstyle, the khajiit passives are very helpful. But more "in your face" players wouldn't see as much benefit, and would probably do better with the redguard passives.

Sorry, that was a long answer just to say "depends", lol. I am a stealth-reliant player, personally, so I like khajiit. My main is a khajiit stamblade. And in fact my stam Templar started as a redguard, but very early on I HATED the huge detect radius, so I deleted him and made a khajiit stamplar because I needed the sneakiness.