Title says it all. The only downfall is not being able to get spells without Arcane Trickster, but minor illusion at first level and invisibility once per long rest at third level really works well with the Rogue. You also get an extra d4 to stealth and performance checks. Is this dragonmarked race better than other races such as Drow?

I'm not sure I'd say it's better.  It's definitely a solid pick.  It's going to really depend on what you want to do.  Performance, in our games rarely comes up.  d4 to stealth is pretty good, but one of the players in one of my current games has played at least 3 rogues, and never has a problem with stealth without bonuses.  So, while it's good on the surface, it might be a bit of a trap because you'd rarely have actually had that d4 make a difference.

If I were going rogue, I'd probably take a long, hard look at a Glasya tiefling...or more likely a high elf with booming blade.

Crazyhawk has a strong point.  A Rogue with Stealth Expertise, a worthwhile Dex score, and eventually Reliable Talent is rarely going to find 1d4 mattering to their stealth rolls.  Performance would come up if you make it come up, but very few DMs call for Performance for anything but actual stage performing.  Minor Illusion is good, but can be done with High Elf or Magic Initiate.  The free Invisibility once per rest is very good, and may be worth considering.

Spells of the Mark adds the given spells to your casting class, which on a straight rogue would require Arcane Trickster.  You gain Charisma instead of Intelligence with Mark of Shadow, and the spells you select still have to obey the selection rules for Arcane Trickster; i.e. you only get a non-Illusion or Enchantment spell at third, eighth, and fourteenth levels. 

Of the Shadow Mark spells, the only standout is Pass Without a Trace.  PWaT, Cunning Intuition, and Stealth Expertise means you can theoretically roll a Stealth check of 51 (nat 20, +17 Stealth Expertise, +10 PWaT, +4 Intuition), and your minimum Stealth roll becomes 38 (10 Reliable Talent, +17 Stealth, +10 PWaT, +1 Intuition).  It's hilariously overkill for the rogue herself, but picking up PWaT could be worthwhile for a Mark of Shadow elf who'd appreciate her party not blowing her stealth rolls for her.

I would posit that Mark of Shadow is good for a base rogue, but not Ultra Super Amazeballs, Take-At-All-Costs.  The free invisibility is pretty baller, but it's not so baller that it outweighs what other classes might bring.

That said...Mark of Shadows is quite compelling for an Arcane Trickster/Wizard multiclass that's taking enough Wizard to get to second-level Wizard spells.  Getting PWaT in your spellbook would be excellent, especially with the extra spell slots to cast it that wizard brings.  Between Trickster, Wizard, and the MI from Mark of Shadows you end up with a huge passel of cantrips.  Not quite as many as a High Elf taking School of Illusion, which is my normal choice for bleeding-edge optimized Arcane Trickster, but plenty thereof and you gain the ability to select whichever school of magic you like.  War Magic is a very potent choice. 

The freebie Invisibility relieves a bit of spell slot pressure, and PWaT lets you get other people past stealth challenges, which rogues are normally kinda awful at.  That's a very specific build, of course, but it could be a fun way to do Mark of Shadows.

I think it‘s a better boost for Rangers than Rogues IMHO.

Heh.  Honestly?

A Mark of Shadows elf rigged up as a Shadow Sorcerer (or a Sorcerer in general, but damn the thematics are on point for Shadow sorcery) sounds bomb to me.

The d4 to Stealth actually helps there, a lot more than it does on a rogue.  You get a Charisma boost, free Minor Illusion, and the d4 to Performance aligns more with Charisma-heavy sorcerers to boot.  The Spells of the Mark list for the Mark of Shadows also has a couple of real gems for sorcerers.  Pass Without Trace, obviously, but also Mislead and 5th level, which is normally exclusive to bards and wizards.  Hallucinatory Terrain is also a wizard-only that Sorcerers could snag via Mark of Shadows, though it's more nichey than either PWT or Mislead.  

That's what I'd do, if I was looking for Best/Coolest Possible MoS elf.

I have to ask, how do you get +17 stealth?

The same way you can get a +17 in any Skill. A character with Expertise in certain Skills (like a Bard for example) can double their Proficiency Bonus for those skills in which they have Expertise. A character level 17 or higher has a +6 Proficiency Bonus. So if they have Expertise in (Stealth) then they get to add +12. If they also have a 20 for their Dexterity Modifier then they get to add an additional +5. 

So that happens late in the game, we won't get above level 9

A Bard gets Expertise starting at 3rd level. Normal Proficiency Bonus at 3rd is +3, and with a Dex of 15 (assuming high stat from standard array and no racial bonus) that Bard could have a +8 to stealth fairly quickly.

A Rogue gets Expertise at level 1, so with a standard +2 Proficiency Bonus and a 17 in Dexterity (assuming high stat from standard array and a +2 racial bonus) that Rogue could have a Stealth of +7 at level 1.By level 9 with 20 Dex (because of two ASIs) that Rogue would have a +13 stealth.