None of them. A nuzlocke run is only hard depending on what rules you follow and what restrictions you place on yourself. The game you do it in doesnt matter. --- Pokemon Platinum FC:3696-5670-3738 Member of the NCG guild.Requests done:111.
My vote goes to Pearl or Diamond. Neither of them are particularly forgiving in the "variety of available doods" department. --- Official Wanderer of the Distinguished Order of Pokemon Veterans FC: David, 3825-0747-5451
Of course grinding forvever makes it easy. Look at all the solo runs running around. One of my rules for Nuzlocke is no grinding to a higher level than the next Gym Leader's strongest mon. --- I ain't licking the sig of a Keyblade that can Rip You a New One (RYNO) and is evil (666)-WiiIsTheChamp People who licks my sig: 48
The way Platinum nerfed difficulty was lowering enemy levels, but some movesets are harder to compensate. If you level-match in D/P, you'll find it relatively easy. Level-matching in Platinum could be more interesting.
That or Yellow, because you could conceivably end up with no way past Brock.