I agree with PId6. Pathfinder Duelist is better then 3.5, but it still mostly sucks. So I'd stick with Pathfinder Rogue.

If it's of any help to you, I had a player who wanted to play a Duelist a while back, so I homebrewed a solution for him. Perhaps it will suit your needs:

Here's a homebrew I made shortly after Pathfinder came out for one of my player's:

The Duelist
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Prerequisites: +5 BAB, Dodge, Weapon Finesse, Tumble 3 ranks

{table=head]Level | Base Attack Bonus | Fort Save | Ref Save | Will Save | Special
1st | +1 | +0| +1 | +0 | Canny Defense, Precise Strike
2nd | +2 | +1 | +1 | +1 | Parry
3rd | +3 | +1 | +2 | +1 | Grace
4th | +4 | +1 | +2 | +1 | Cunning Reflexes
5th | +5 | +2 | +3 | +2 | Acrobatic Charge
6th | +6 | +2 | +3 | +2 | Riposte
7th | +7 | +2 | +4 | +2 | Elaborate Defense
8th | +8 | +3 | +4 | +3 | Evasion
9th | +9 | +3 | +5 | +3 | Advance
10th | +10 | +3| +5 | +3 | Crippling Strike
[/table]

Canny Defense (Ex): When wearing light or no armor and not using a shield, a duelist adds 1 point of Intelligence bonus (if any) per duelist class level as a Dodge bonus to her Armor Class while wielding a melee weapon. This bonus stacks with all other Dodge bonuses. If a duelist is caught flat-footed or otherwise denied her Dexterity bonus, she also loses this bonus.

Precise Strike (Ex): A duelist gains the ability to strike precisely with a light or one-handed piercing weapon, adding her duelist level to her damage rolls. When making a Precise Strike a duelist cannot attack using two hands or use a shield. This restriction also applies to the duelist's Parry, Riposte, Elaborate Defense, and Crippling Strike abilities.

Parry (Ex): Whenever you or an adjacent ally is attacked by a melee or ranged weapon, you may attempt to Parry it as an Immediate Action. If you choose to use this ability, you must declare that you are using it after your enemy successfully hits but before the DM announces damage or effects of the attack. Make a melee attack roll, adding your Intelligence modifier as bonus to hit. If your modified attack roll is higher then the enemy’s modified attack roll, the attack is negated.

Grace (Ex): Any Dodge bonus that you possess from any feat or class ability now applies to all enemy attacks against you. You no longer need to "designate" one foe. This includes the AC bonus, as well as any special abilities or feats that rely on the Dodge ability, such as the Elusive Target or Defensive Throw feats. In addition, you may add any Dodge bonus to AC that you possess from any feat or class ability (such as Canny Defense) as an Insight bonus to your Reflex Save as well.

Cunning Reflexes (Ex): You gain Combat Reflexes as a bonus feat. If you already have Combat Reflexes, you may choose any other feat that you qualify for in it's place.

In addition once per round as a free action you may add your Intelligence bonus as a bonus to hit on any attack of opportunity.

Acrobatic Charge (Ex): When you Charge you are not required to move in a strait line. You may make as many turns and changes in direction as you like, within the limit of your doubled movement rate. You may also Charge over difficult terrain, through occupied squares, or by swinging on a rope/chain/etc in the direction of your enemy (though you may still need to make appropriate checks to successfully move over the terrain). You also gain the Pounce ability (you may make a full attack when you Charge).

Riposte (Ex): A duelist can make an attack of opportunity against any creature whose attack she successfully Parries, so long as the creature she is attacking is within reach.

Elaborate Defense (Ex): You gain Improved Disarm as a bonus feat. If you already possess this feat, you may choose any other feat that you qualify for in it's place. In addition, once per round as a Free Action when an enemy attacks you and misses (either because it failed to hit your AC or because you successfully used Parry to block the attack) you may make a Disarm attempt as an attack of opportunity.

Evasion (Ex): You gain the Evasion ability. If you already have the Evasion ability, you gain Improved Evasion instead.

Advance (Ex): Whenever an enemy within your threatened area makes a 5 ft step, you may also make a 5ft step as a Free Action. This does not prevent you from moving normally or taking another 5ft step on your turn.

Crippling Strike (Ex): Whenever you successfully use the Precise Strike ability and confirm a critical hit, you also deal 1 point of Dexterity damage and reduce all of the target's movement speeds by 5 ft (to a minimum of 5 ft). The movement penalties from multiple Crippling Strikes stack, and each penalty lasts until the target has repaired the Dexterity damage from the Crippling Strike that imposed it. Enemies that are immune to critical hits or ability damage are immune to this ability.