Weapon Choice and Feat Maximization
What combat feat is most effective? Well it really depends on your play style. If you prefer debilitating your opponents before taking them down, it's most effective if you become a scoundrel-guardian wielding a double-bladed lightsaber. On the other hand, if you like to have your strength buffed beyond mortal levels, then wield a decked-out lightsaber in your main hand and Baragwin Assault Blade in your off hand and use Critical strike to do insane amounts of damage. If you prefer the to go the more straight forward approach, without the frills of sneak-attack damage, the fickle nature of critical strikes, and the need to have strength up the yin-yang, Power attack is recommended.
Flurry is your friend. In the right circumstances you can do more damage than any other combat feat, assuming you can perform a sneak attack. However it is the only combat feat that hurts both attack and AC, which means that this can spell death at low levels. Also it is the weakest of the three if your weapon does lousy damage. Summary: Worst at first, best at last.
Critical Strike is great fun. In the right hands Critical Strike can do more damage than any other combat feat (assuming that you don't have any source of sneak attack damage). This feat even helps at lower levels, as it only reduces AC, and not attack, meaning that you'll get in more damage, quicker. On the other hand, for weak builds this is not recommended, and its fickle nature may turn off some who want more reliable damage. Summary: Fun but fickle.
Power attack is helpful in that it is the most versatile of the three, as it does maximal damage for all charaters of low to mid levels of strength no matter what they wield. 10 damage may not sound like much, but if you think about it it is the equivalent of adding 20 strength worth of damage! It is the best feat when it comes to combat for any character that is more defensive in nature. The real downside is that the attack penalty at lower levels really hurts, and causes whiffs more often than not. Summary: Versatile but at the cost of power (ironic considering its name).
If you truly want to know what feat and weapon selection do the most damage in your circumstances, then you can use my Damage Calculator which can be downloaded here. This is an zipped excel spreadsheet so you need to have Microsoft office or some other XLS viewer to be able to use this. An Open Office version can be downloaded here.
For more on lightsaber crystals and their properties click here.
On the off chance that you decide to wield blasters, then there is only ONE FEAT that is any good. That is rapid shot. The other two remaining ranged weapon combat feats are completely gimped, as they only get two attacks per round, regardless of whether you use the Master Speed force power or not. Rapid shot, on the other hand, can get upwards of 5 shots in a single round, meaning that it can be quite powerful in the right hands.