This isn't really a question of which is the best medic, but which is your personal to favorite to play? Your's doesn't have to be ranked, but mine will be.
5. Sawbonez- Sawbonez is just boring to me. Throwing around health packs may the best thing for your team, sometimes, but I dunno. He's just too... "unfulfilling". I mean, I've had fun playing as him, don't get me wrong, but just not as much as fun as the other medics.
4. Sparks- I'd probably find Sparks more fun to play if I had good aim. I usually find more enjoyment running around melee-only, rather than popping heads. When I do land those headshot, though... FeelsNutWorthyMan...
3. Aura- I've never really been a fan of static deployable type of gameplay, at least when on attack, so Aura used to be that medic I would really only put in my squad in the chance that I would have to play her on Chapel or Underground defense. Now, I still kind of do the same, but she's more of a merc I play when I'm actually in the mood to play her (or if I have a mission for her, obviously). Running around with a shotgun and turning people into Swiss cheese, will always be fun though.
2. Guardian- Despite being the worst medic, and still pretty new so changes are sure to be coming, I have way too much fun playing her. And that's because she encapsulates the feeling of Dirty Bomb for me perfectly. Always multitasking, always at the disadvantage of not being able to heal, always running around trying to keep everyone alive without being able to heal them, getting those clutch multi-revives, just hits me right in my dopamine. Best of all, her static defense can still be very good on attack, since it can be useful in multiple situations.
1. Phoenix- The Undying Spaniard himself, Phoenix is my favorite Medic to play. He combines everything I like about Aura, Sparks, and Sawbonez while removing what I don't like about them. Aura has AoE healing (if you knew my main in Overwatch, you'd know I really like AoE healing), but is a static defender. Sparks has instaheals, but heals very little and only heals one at a time. Sawbonez has awesome weapons, but single heals that can be stopped with damage is just straight not fun. Phoenix has all of those positives, but no negatives. He's a jack of all trades, master of none, and nothing pisses of an enemy more than nearly winning a team fight and then a fruit-obsessed Spaniard suddenly healing everyone and winning a team fight. Getting defibrillator kills are always fun, and reviving a teammate under enemy fire is just as fun. He may not be the only one who can do that, but he's pretty damn good at it. Oh and self-reviving during an intense fight hits me right in my dopamine too.
And that's that! Let me know your list!