Fletcher seems to be the most obvious option for pub play, although it’s not on your list of mercs to add. (The high utility and damage output of his stickies is amazing, coupled with his status as an engineer.)
Pheonix seems to be less team-oriented than another medic such as Sawbones, but if annoying the enemy team is the goal, then by all means, choose Pheonix.
Phantom post-nerf is underwhelming, and you would honestly get more kills with Proxy. 1 head shot with a shotgun does more damage than phantom’s sword swings with less time-to-kill.
Proxy has more speed, and access to mines which can be far more useful. All of this and she’s an engineer: allowing for better team-play.
Nader is generally good for area denial if her nades are used conservatively, even if they can’t be cooked to confirm direct damage with every shot. She’s also decent at destroying deploy-able abilities such as mines and turrets.
Fragger seems a good option as well, despite not being on your list. Learning to cook his nades almost always will confirm a kill each time you throw one.
The choice is yours, really, although all the mercs on your initial list seem to be a bit selfish and less team-focused;
Sawbones is more team-friendly than Pheonix
Proxy is faster and an engineer: unlike Phantom
Nader is generally good in most battle situations, but doesn’t supply ammo to your team, whereas Stoker may be a good option, honestly.
(just my opinion)