I ended up going with a Shadar-Kai pure Rogue because of Shadow Jaunt. Shadow Jaunt is so ridiculously core to my playstyle now that any pure Rogue I play in the future will likely have to be Shadar-Kai, but I'll elaborate on that more a bit later.
Assassinate is obviously core to the playstyle- I solo a lot and the ability to stay in stealth is the greatest boon to a solo stealther. Mobs often gather in groups of two and taking them both out with assassinate is a skill very easily mastered- even if they don't come in pairs, assassinating from behind them yields the same result with no detection, while skipping the mobs entirely is also very easy.
You generally want to clear out mobs if it's not inconvenient so you can create a place to hide if needed. Skipping encounters is fine too as long as you are always thinking of safety nets. Playing a solo Rogue in DDO is by far the most satisfying sneak experience I've ever seen, and the amount of things you have to manage is absolutely perfect. It makes it feel more like a craft or art than anything else.
None of my Rogue experience could be possible without Shadow Jaunt specifically, and to a lesser extent, whirling chain and gloom stalker. A Shadar-Kai Rogue is exceptionally more powerful within my playstyle and here is why-
Shadow Jaunt is a fantastic tool for skipping encounters or getting behind groups- only rivaled by a similarly sneaky ninja who has abundant step and (permanent) shadow fade with the right enhancements. The edge that an assassin has over a ninja is that the assassin's insta-kill keeps you stealthed- quivering palm does not. Shadow Jaunt also is the ultimate disengage. Unless a mob has true seeing, you'll be out of there immediately and they're more than likely not going to be able to find you, giving you another shot at what you failed previously.
Whirling Chain is the ultimate hail mary. Popping Uncanny Dodge along with Whirling Chain will save your life when you get caught. And you do occasionally get caught- and caught without Shadow Jaunt. Uncanny Dodge turns you into a dodge tank during it's duration, and Whirling Chain provides you with more tanking ability as well as a great amount of sustained AoE damage to burst down the group you've gathered by being caught. You still have casters and archers to take care of, but you can now move around to do this and won't be followed by a thousand melee mobs.
The Ranger as well as the Monk both have spammable powerful tools of making a mob susceptible to sneak attacks. I've never seen a failed unbalancing strike, even though it does have a save, and ranger's have exposing strike, which is a no-save "hey, you're going to be SA'd to death now" ability. Rogues have the daggers as well as bluff- but these aren't nearly as reliable. This is why Gloom Stalker is great- regardless of whether or not the mob sees you, any attack out of stealth makes them vulnerable to sneak attacks. This has no save, and works on bosses. Going in and out of stealth to trigger this is faster than throwing a dagger or a bluff attempt- rendering the other options useless in a 1v1 situation as they both have saves, and this also triggers on assassinate.
My assassin is my only character than can solo elite Running With Devils at level 16- none of my characters have stunning gear, assassin included, but being able to get through that quest without a horrible and painful death from the Glale's, stalkers, and Wisams is a huge accomplishment for me since every one of my characters have generic gear, and is on their first life.
If Shadar-Kai Rogues did not exist, a Monk would be my choice for sure- but because they do and have an answer for a good amount of the Monk's advantage, an answer for the Ranger's advantage entirely- Whirling Chain, and considerably more sneak attack damage-a Shadar-Kai assassin is the only assassin for me.