Couple things here:
-The odds of Surfer buffing Superman with the Power Cosmic via cosmic awareness are as likely as him using cosmic awareness to debuff Superman if he were to fight him. It's not his M.O. as a rule and Surfer hardly every displays the kind of feats on a regular basis to argue him doing that in character. To that end, it's more likely Loki amps Thor (as he's done so in the past) than Surfer would amp Superman.
-Loki is, at worse case scenario, a Mid Herald who's more than capable of giving Thor a fight. When things get strictly physical, Thor holds a significant edge, obviously, but Loki isn't some weak feeb who can be easily one shot or anything under most portrayals. Thor also has the benefit of having a borderline plot device weapon designed to counter most of Loki's mystic assaults. Loki would definitely be a troublesome foe for either Surfer or Superman and anyone who disagree is either not all that informed on Loki (which happens from time to time) or trolling.
All that said, I'm undecided.