Ah 69 - the sexiest number and the most mutually-pleasurable sex act, right? I mean, you both are orally pleasuring each other SIMULTANEOUSLY - what could be better?
Oh right, more or less anything, since 69:
But hey! At least your neck will hurt afterwards and you both would have been much happier with giving each other oral individually.
Sex in the shower - it's both dirty AND clean! The best of both worlds! Except, uh, it's not good for anyone who wants to enjoy the sex, since you're mostly focusing on:
Making standing sex work and be comfortable (which it never is)
Not slipping and breaking your neck
Making sure the water temperature is perfect for both you and your partner
It's that last point that really is the nail in the coffin for shower sex - very few people share an exact similar ideal shower temperature. Some people like it real hot, some more lukewarm, and others (aka monsters) kinda chilly. And awkwardly trying to negotiate the right temperature DURING sex is not going to make either of you enjoy the process more, especially when there's a decent chance one of you might slip and seriously injure yourself.
So - who do you want to be in this situation, the person pressed against a wall (either with your face mashed against it or constantly bumping the back of your head against it) OR the person who has to stand in front of your partner and mash them and/or carry their weight (if you're doing that thing where you hold them in your arms while sexing them against the wall)? Neither are very pleasant, but it definitely looked pretty hot in that episode of Grey's Anatomy you guys watched like four years ago, and that's why you should never take sex lessons from Shonda Rhimes shows.
Oh cool, the blowjob-giver gets to crouch and be on their knees while having a dick in their throat, while the receiver is just standing awkwardly with no idea of what to do with their hands.
Seriously, what do you do with your hands there? Just let them hang to the side? Hands on the hips? There's no good position for your arms (and the answer is DEFINITELY NOT TO PUT YOUR HANDS ON THE BACK OF THE GIVER'S HEAD, FYI).
Couch? No. Floor? No (although hardwood, linoleum, and carpet all are different experiences). Desk or table? No. THE GROUND? ABSOLUTELY NOT.
Beds are perfect for sex - soft, broad surfaces with springs in them. Why mess with that perfect situation and go for something hard and flat or kinda gross (there's crumbs of SOMETHING in your couch right now, I guarantee it - and I don't want my genitals near crumbs).
Just have sex on the bed, in a way where both of you can enjoy yourself. It's not complicated.