Im planning to make a Dexy Lvl 5 character using paladin and rouge and Im stuck between the two 

I can either go :

Paladin 3(conquest) + Rouge 2

Or Rouge 3 (assassin) + Paladin 2 

What do you guys think

I’d go Rogue 3 + paladin 2

Before I could properly answer I'd need to know more about the character you intend. 

Why is the Rogue going the route of the Paladin?

Why would a Paladin go the route of the Rogue?

Given these two questions RP wise it makes more sense to go rogue then Paladin and opposed to a Paladin going Rogue.

its a one shot but both ways are fine Im mostly thinking of an optimal build

From optimal perspective though it more depends on what you want to optimize. 

The ability to instill fear or sneak damage.

From a DeX based paladin for a one shot I'd say 3 rogue 2 paladin would be better.

what feat would you guys recomend between these:

Magic initiate

Sharp shooter

Luck 

Athlete 

Between these I really wouldn't recommend any of them for a Paladin let alone a multiclass Paladin.

That all being said if you had to pick one it would only be luck.