Going down the list:
HQ: A shas'el will always be the best. Aun'va is worthless as are the regular ethereal s (wait, I only get to use their ability if I have line of sight... but if they die then my whole army has to take a morale check??!?! If they had left the rule that allowed you to use their special ability whether you can see them or not)
Shadow sun has an ability that is really good mixed with weaponry that is worthless for what she needs to be doing. Why would you give a character a short ranged weapon with tech and abilities that you want to keep back?
O'shovah is insane, but you have to build around him a lot. Add to that the loss of units and reduction of others and its one of those coin toss characters... His abilities are ok, though I think I would rather have his old rule that allowed him to make his entire army good against any army, not just the orks...
Shas'o are really good, but point intensive. In smaller games you are better off with an 'el, but in larger games (1850+ ) that extra 25 points can be worth it.
As for whether or not to take bodyguard... Depends on the role of the commander. I personally like to take them in any game over 1500 points, but then again I like a crisis suit heavy army.
Elite: Crisis suits should be mandatory. You can take them as infantry hunters, MEQ killers, tank hunters. Versatility makes them more than worth their point cost/small sized squads. Personally I stay away from the burst cannon, and I've never been a fan of the flamer (though I am getting ready to build a unit of three twin linked flamers, I just need to get the models and decide what their third hard point should be...)
Stealth suits are alright. I prefer the xv15 over the xv25, especially since I have 6 of them...
. I do believe that if you are going to take stealths to make sure of two things. First, the fusion blaster in the unit is worthless. One for every three when unit size is 3-6, it reduces the effectiveness of the unit and removes up to 6 burst cannon shots... Secondly, the full 6 man unit should be preferable over the minimum 3 man unless you are so low on points that you can't afford them. With the full six man squad you have to lose 4 before you are under half, and you get 18 shots.
Troops: Unless you downloaded the rules for Gue'vesa you only really have two choices.
Firewarriors, you have to have at least one unit. Which is good since they are good shots, have the longest range basic gun in the game (by which I mean is carried by troops with no upgrades) and it is higher strength than most other basic guns. Add to that a pretty good armor save and the ability to get some of the best grenades possible (photons are insane and I always take one suicide unit with carbines and EMP's) Then add the ability to take one of the best transport vehicles in the game and you have a unit that is very powerful.
Kroot on the other hand have the one thing that the rest of the army lacks... close combat ability. I'm not going to lie and say that they'll take out a greater daemon by themselves, but they can tie it up for a turn or two until the rest of your army can point a couple of really big guns at it. Then you take into account their infiltrate and their pets. A unit of 16-20 with a full unit of hounds will make even a large genestealer unit think twice about charging them...
Fast: Lets get this out of the way first. Vespids are only good for one thing, MEQ killing. And they aren't even really good at that. At most you'll get one good turn of shooting, after which plan on losing the unit. I think I'd rather spend my points elsewhere thank you.
Piranha are good, though I still haven't decided if they are worth me losing a slot to them. I can see taking a full 5 man unit as it will also give you a 10 man unit of drones. Plus spamming burst cannons, or having single units for tank hunting can be good... I don't know, I'm still on the edge about this unit.
And the reason I'm on the edge is my infatuation with pathfinders. I love these guys, scout and markerlights are always fun. Plus you basically double your fast attack choice as they must be bought with a devilfish, which I always upgrade to warfish just for the number of shots that it gets (7 strength 5 shots... why would that be a bad thing?). The markerlights are one of the best guns in the game... I can reduce your cover save, your leadership, send a seeker missile at you, increase my own units ballistic skill... so versatile its not even funny. I always take two units maxed out. If you want to know why then ask my opponents, they always seem to go after them first...
Lastly there are the drones. I love drones, twin linked carbines are always good, pinning tests being forced upon the opponent (see the pathfinders for why thats a good thing) and the ability to deepstrike... All for a relatively cheap points cost. I've been known in larger games to take at least one unit of these just for the look on my opponents face when he realizes that unit of drones just wiped out 4 times their points cost (markerlight + seeker missile into a rhino containing a very expensive Wolf Lord and retinue which had been surrounded by drones... needless to say no one could get out...)
Heavy: Broadsides are probably my second favorite unit (pathfinders being first). Good stats, excellent save, multiple wounds and the nastiest gun in the game (twin linked of course). Whats not to love? And now they can take an Advanced Stabilization System, so that they can move and shoot? Unless you are a fully mech army there is no reason you shouldn't have at least one unit of these in your army. Heck, even a fully mech army should have one unit!
Hammerheads are the other essential. Having the ability to be a tank hunting monster or an infantry shredder with some of the protection upgrades it has is just soooooo good. I personally love the railhead version over the ion cannon, but I think thats more to do with the fact it can use submunition, which has the potential to kill a lot more than the 3 possible with the ion...
Drone controller with sniper drones are alright, I definitely can see potential. I just don't know if I want to give up one of the precious heavy slots for a unit of 9 (thats right, 3 whole units in one choice... I wouldn't even consider only taking one as their ballistic skill and what I need them to do definitely require more than what one is capable of doing).
SkyRay... Honestly, I've tried it in a couple of games and all I can say is: Buy the skyray for the hammerhead and extra bits, because its not really worth it in game... Six seeker missiles are good, but with my pathfinders I find those almost always get wasted first turn, and the mobile markerlights are decent... except I already have 16 markerlights... no need for two more really... And yes I know the tactics associated with the skyray, keep it behind cover until all the seeker missiles are gone... Still not worth it.
You'll notice I didn't use any forge world units, nor did I remark on the Gue'vesa that much. I don't have the rules for the forge world units and I don't plan on buying a unit of guardsmen to convert (though I am thinking of getting some skaven or beastmen to convert over). I also don't plan on ordering from forgeworld because of costs. Though I might change my mind later, as of right now I'm more into getting more models to make a fully apocalypse ready army (might even buy the crisis suit heavy box and the box that has the 3 tanks....)