Im trying to decide if I should use on of these as a # 4 starter or find an alternative.

Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Hal McMasters

Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Tony Cordero

Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Dustin Worley

I don't see Cordero making it in the rotation but you could use McMasters and Worley as a tandem.  Neither is that good but you can minimize Worley's vL by having him come in relief against lineups stacked with righties to face McMasters. 
Since McMasters won't be able to work deep into games by himself this will help get you 7-8 innings between the two.

If you can't afford to carry both then you might want to find another option.

McMasters is way overpaid and I'd rather not have him on a ML roster but if your forced he might survive as a SuB,  Cordero would be ok as LRB but if he started getting chewed up I'd send him to the minors never to return.  Worley would be a decent LRA and could chew up some innings as a #5.  In my opinion.

I signed Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Cookie Mesa would he make a better #4?  I only run 4 man rotations

Yeah I think Mesa is better than the other three guys

I agree with toy, he's better than the other 3 options you've posted