Depends a little bit on your party composition too. If you have a warlord in the party who can allow for a lot of mobility, you wouldn't need Deft Strike quite as much, in which case I'd go with Piercing Strike and Disheartening Strike.
If you have no Warlord, and a Wizard who likes to use Illusory Ambush, then Deft Strike instead of Disheartening Strike would be the way to go.
Also if you get ample flanking opportunities from your allies and other attack boosts from a cleric or warlord, and have Nimble Blade, then Piercing Strike might not be quite as necessary, and the mobile nature of Deft Strike, and defensive nature of Disheartening Strike may be better.
And as mentioned, retraining is an option every level. So at first level, just pick whichever powers you feel will let you survive better, and you're good to go.
On an unrelated note, I don't much like melee rogues with no Con bonus. They run out of healing surges way too fast. As a matter of fact the first (and so far only) casualy in the game I'm running was a rogue with no Con bonus.
If you have no Warlord, and a Wizard who likes to use Illusory Ambush, then Deft Strike instead of Disheartening Strike would be the way to go.
Also if you get ample flanking opportunities from your allies and other attack boosts from a cleric or warlord, and have Nimble Blade, then Piercing Strike might not be quite as necessary, and the mobile nature of Deft Strike, and defensive nature of Disheartening Strike may be better.
And as mentioned, retraining is an option every level. So at first level, just pick whichever powers you feel will let you survive better, and you're good to go.
On an unrelated note, I don't much like melee rogues with no Con bonus. They run out of healing surges way too fast. As a matter of fact the first (and so far only) casualy in the game I'm running was a rogue with no Con bonus.