I have a Troll Shadowknight myself.
For Shadowknights, I would say the Troll/Ogre debate comes down to what you prefer to do: Soloing or Grouping. If you prefer to solo, the Troll regeneration will give you a lot more benefit than FSI.
https://wiki.project1999.com/Blood_Ember_Greaves and
https://wiki.project1999.com/Death_Peace will give you plenty of FD opportunities before you die in most cases.
The inability to use
https://wiki.project1999.com/Blood_Ember_Greaves ,
https://wiki.project1999.com/Blood_Ember_Boots , and
https://wiki.project1999.com/Blood_Ember_Gauntlets makes me dislike Iksars, even though they have racial regen as well. They do get
https://wiki.project1999.com/Greenmist , but I think it is a little over hyped myself. It is nice to be able to stack Epic and Greenmist procs. However, due to both DoTs having a fairly short timer, that stacking isn't as common as one would like. Whenever the DoTs aren't stacked, Greenmist is just a not quite as good Epic.
If you prefer to group most of the time, FSI is usually the better racial. It maximizes your ability to maintain agro, and adjust to changing situations. Yes, you may not regenerate quite as fast after a bad pull, but you will regenerate pretty fast with a
https://wiki.project1999.com/Fungus_Covered_Scale_Tunic , and you will probably have a regeneration spell on as well if one of your group members can do it. Grouping generally speeds everything up, since you will generally have buffs and heals.