In this video, would it have been better if the pilot had attempted a tail-strike landing instead of a normal flare?
While there probably is an "ideal" attitude to impact water, and it would be nice to crash-land with exactly the correct attitude... it's very much a secondary consideration.
By far the most important thing, when landing on water, is to land slowly. As such, your aim should be to land (/crash) with whatever attitude gives the lowest possible ground speed/descent rate at the point of impact. If that means a "normal" flare, do a normal flare. If that means a harsher flare with a tail strike, do that instead.
The point is that you're in an emergency situation, and your biggest priority is to get the speed right: you likely don't have the luxury of trying to fine-tune your angle of impact and flare. Additionally, you always have the risk of over-flaring and stalling into the water instead, which is a worse end result.
So yes, it may - with some airframes - be beneficial to have a tail strike, but you're far better off just keeping the aircraft under the best control possible and reducing your speed as far as possible
Having your tail hit the water first probably isn't the best idea. Remember, impacting the water will slow your plane down very quickly, which will take away all the lift your wings are generating. Thus, it would likely drop the front of the plane into the water, possibly at a very high speed. It would be preferable to avoid such an impact.
The best practice would be to land as slowly as you can (like Jon Story said), while doing the best you can to keep the plane level with the water (though, as Jon stated, that would be a secondary consideration to keeping the speed low.)
It's pretty dependent on the structural integrity of the airplane, and water-landings aren't an exact science to begin with. If the tail of an aircraft can withstand the sudden deceleration of striking the water without breaking off, then a tail-first landing should be ok, if the AoA is still close to level. This will ensure that the aircraft doesn't flip tail-over-nose when it does finally settle in the water (if, for example, the "landing" speed is too high). Put the tail in the water at too high of an AoA though, and the sudden deceleration of the tail will cause the nose to slam into the water quickly. Alternately, it can break the tail off the aircraft. This would allow water to flood into the aircraft, causing it to quickly sink. Definitely not optimum if you have passengers to evacuate.
A fixed gear aircraft like that in the video will almost certainly flip over no matter what technique is used. The main wheels are well below the aircraft's center of mass, are going to contact the water while the aircraft is still moving forward at a significant airspeed, and will create a very large drag force as soon as they do. It all adds up to an upset moment far larger than the tail can counteract, so the aircraft will at the very least upend, if not rotate all the way onto its back as in the video.
The picture can be more favorable for a retractable gear aircraft if the wheels are up at ditching. Even then, it's possible for aquatic drag forces to create a large enough pitching moment to cause the nose of the aircraft to "dig in".
Touching tail first will probably make little difference. For the aircraft to settle rather than slam onto the water, the wings have to be generating enough lift to support it, which means the aircraft still has to be at flying speed at the moment it contacts the water, which means huge drag for whatever is in contact with the water.