Ok I took another look. Toxic Haze is neither spreading Corrosive Dart for me in MM FPs, nor is it dealing any damage! Corrosive Grenade doesn't do any damage either!

Ah, so it's the sniper one. Right, so Toxic Haze spreads it for operative.

Can confirm Corrosive Grenade is not spreading Corrosive Dart on my Lethality Operative in MM Flashpoints.

I've done it a lot of times in a mix of Tionese and Columi and as a melee DPS at that. As others have already said, it's very execution based.

You need to go to the mission terminal in the supplies section of the fleet to get the quest which rewards you 99 tionese comms. EDIT: that's some fast ninjaing ^^

Assassin has stealth and otherwise great utility, but has crap AoE. Sniper, on the other hand, can have quite good AoE, and I've found that good AoE makes the leveling process much faster, despite not being able to stealth missions for just their objectives. You won't be able to solo heroics with a sniper to the degree you could with an assassin though, primarily because of assassin's superior mez capability.

While a shadow tank really is the best tank for soloing and can survive anything while doing decent damage, he has crap AoE until 40 when it gets ok, but not great. While arguably not worth much in the endgame, good AoE will speed up your leveling process dramatically. The shadow is actually quite a late bloomer in other regards too, and that's the primary reason why I wouldn't recommend it as a first character. Instead, I'd go for a trooper commando as my first pick and a consular sage as my second. Both have excellent AoE capabilities and can heal themselves and their companions, but the commando blooms much earlier - as soon as lvl 10 in fact, when you get a nice spammable AoE in addition to the very high damaging but on a longish cooldown one which you get even earlier. A sage, on the other hand, gets his first AoE at lvl 20 and his second at 34. However, I think they're a bit stronger than the commando's. Another benefit for the commando is that you can pick armormech as your crafting skill and have up to date armor for yourself and all of your companions except one, as they use the same armor that you do. And since you have some heals too, you're not as dependent on medpacks like other classes so biochem is not a highly attractive crafting skill as it normally is (this also goes for the sage).

If you're doing pretty much anything except spamming DS for procs on a shadow you're horribly force-inefficient and your fights will take longer because of that. The exceptions are Slow Time, Force in Balance, and Whirling Blow at 4+ targets, but the latter is so horrible that you'll kill a mob faster by killing targets one at a time via DS procs or ST/FiB. Taking AoE on a shadow is ok once you're at 40+, but the OP wanted advice about solo questing. That you'll be doing while leveling (I don't consider dailies for that because.... argh) and there's a long way till 40 if you solo. Shadows really are super easy, but you have to be ok with a very simple rotation that doesn't change much as you level or you're gonna bleed boredom through your every orifice. If that's your cup of tea by all means go ahead, I thought I'd like it simple too but got burned out by it very quickly.

As someone whose first lvl 50 was a shadow, I can't stress this enough - DO NOT GO WITH A SHADOW! Until the very last levels, shadows are utterly boring and tedious to play. They have the worst class design ever, with everything being based on procs off a single skill you get at lvl 1. You won't be doing anything except Double Strike, Double Strike, Double Strike, oh look a proc - something else, Double Strike, Double Strike, Double gaaaaaaah!1!!!! Up until 20-30 you won't even have anything to proc decently and without procs, Double Strike is your most efficient attack in regards to damage per point of force after TK Throw (which is easily interrupted) and Force in Balance (which you have to trait for and it has a longish cooldown). So unless you really don't mind a boring as hell rotation, don't go with a shadow. Also, shadows probably have the worst AoE capability in the game, and that's extremely important while leveling. On the other hand, I can't recommend sage and both knight advanced classes enough. All three of them are loads of fun to play and much more powerful than a shadow during leveling. Shadows are fine as tanks at 50 and as DPS if you can stomach their rotations, but for leveling, they are abysmal.

Indeed, while I've lost most of my names, I've had the opportunity to rename two of my toons with better ones!