It is likely that all of the 2C-x compounds have similar levels of toxicity, with the 2C-halides (I,C, and B) being indistinguishable in this regard and the 2C-alkanes (D, and E) likewise being comparable in terms of toxicity. These simple 2C's are generally accepted to have a low level of toxicity. To give you a ballpark idea, they are likely somewhat more toxic than most tryptamines and lysergamides, and definitely less toxic than MDxx and bk-MDxx compounds for instance.
The 2C-T-x (thioalkane) compounds are considerably less safe than their simpler substituted cousins, and most have at least some deaths associated with their use (usually in combination with one or more strong stimulants). I believe that this is because they exhibit selective monoamine oxidase inhibition, which can cause a hypertensive crisis in high enough doses/combinations due to the contraindicated stimulant + MAOI effect.
The dihydrofuran and tetrahydrofuran 2C's ("flies" and "dragonflies", not necessarily respectively) are far less researched than the 2C's lacking the tell-tale wing structures. I would stay away from these. They are very potent, and it appears much more toxic than the earlier generation 2C's.
The alpha-methylated 2C's (DOB, DOI, DOM, etc) last a LOT longer and are a LOT more potent than their phenethylamine counterparts. I would suspect that they are also considerably more toxic, although I would speculate that this is to a lesser degree than with the flies and dragonflies.
The alpha-methyled, winged 2C's (Bromo-Dragonfly and the like) are VERY VERY VERY TOXIC, and have been known to cause severe adverse reactions including deaths in the accepted dosage range of the first-gen 2C's. It seems that Shulgin got it right the first time, but you can bet that China is going to continue churning out increasingly toxic substituted phenethylamine varients until they produce something so toxic that you can die just from looking at it, at which point all of these wonderful RC's are going to get scheduled, but I digress.
So, to answer your question, 2C-B is well researched and is believed to be safe. A little knowledge of chemistry and neuropharmocology will tell you that this means that 2C-I and 2C-C are also safe. 2C-E has a pretty well documented history of use, with little to no reported health problems caused by its use. By associative corrolary, 2C-D would have a near-identical safety profile to 2C-E. These are all a pretty safe bet. And to reiterate, if safety is your highest priority, then the 2C-T-X compounds should not be your first choice, although for a healthy individual who is using them responsibly, they also pose a pretty minimal risk. And it is apparently not that good for you to eat flies, so hydrofuran rings and safety seem not to go hand-in-hand when it comes to psychedelic phenethylamines.
Time to pass out for the next 20 hours.
Saucy out.