Alright. Since noone here is giving you a legit answer, let me give it a shot.
1. Snowboarding: Safest on the knees, that's about it. When it comes to backcountry, I would not choose to snowboard. If caught in an avalanche your board will suck you down and pin you if you buried.
When it comes to snowboarding in the park, I find there is a lot less variety of tricks because switch is no big deal on a board and you can't do crosses.
When it comes to powder, boards have nice floatation and can be freaking awesome. When it comes to moguls... (face-palm). Boarders can do steeps, it's not as easy though so you don't see as many around steep bowls and shoots unless there is powder.
2. Telemarking: Safer on the knees than skiing but you might get a ski in your face when you fall. Just like a snowboard, telemark skis will drag you down and pin you in an avalanche. If you fall on the slope, well, you have over a 40% chance of getting tangled up and looking stupid trying to get back up. The bright side about backcountry with these is you don't need backcountry boots or bindings, just get your skins, transceiver, shovel and probe.
I admire telemarkers because they choose the hardest of them all. When you make your turn, bringing one leg down puts a lot of strain on the thigh and it takes a lot of strength to do it all day with skill. When it comes to jumps and bumps, telemarking isn't so great. The skis hang down in mid air with no heel piece and they are hard to maneuver in tight bumps. Telemarking isn't for speed but you can cruise along steeps and groomers with good speed.
3. Skiing: Worst for knee injuries. In the backcountry, these are the most costly set up but the safest in case of an avalanche.
As we all know, there is a lot of diversity in skiing, given the right setup, you can ski almost any terrain. Skiers can handle bumps with prestige; the excel in steeps with a wide stance and hop turns; lot's of different tricks in park and pipe; you can go super fast and in control; you can cruise through powder; etc.
When it comes to which is the best. I opt for skiing.