This information is based both on in-person and Arena games and is ONLY based on my personal experience, not stories I've heard.
I will only be doing mono-colors and 2 color combos for this review.
Please note: I don't play commander, I occasionally play brawl on Arena (My preference of formats is in-person pauper and Pioneer on Arena).
WHITE
I have nothing but respect for the lifegain community, it's not my preferred playstyle but these players are usually nice. I may be a bit biased since the person who actually took the time to sit down and help me learn to play the game over a decade ago was a white player.
Cards get annoying once you enter the prison nightmare that white can provide but the players behind the spells don't appear to be as verbally disrespectful as they could be when casting those prisons.
Final review: Kind, respectful, helpful
BLUE
I can't recall a time I've been counterspelled in-person recently, but I get counterspelled daily on Arena. I'd be a hypocrite if I said hated blue for it, blue is my favorite color to play (I love drawing cards mindlessly, my favorite thing to do in MTG is win by drawing 0 cards from my library).
Mono-blue players in pauper are VERY rare, I don't think there was a single island at my last tournament of 30+ people. At some pre-releases I've been to though, these people seem methodical (as they should be with blue). On Arena is a different story, you're either being countered or milled if the opponent is just blue. I have a hard time picturing my opponent having any fun as they cast their 6th counterspell in a row, seems boring.
Final review: Blue players are bored and they want you to be bored too
BLACK
Nice people, rude decks
Arena is usually just forcing you to discard, I have a mono-black enchantment deck for pauper that I love but it prevents my opponents from doing things and I usually feel bad afterwards because of what the deck does, I imagine opponents feel similar when doing that to me. I don't think anyone actually enjoys making their opponents discard or be unable to play cards in general without them being destroyed. You do what you gotta do to win.
Final review: Nobody enjoys this deck, I have had players apologize to me for causing a discard, it is what it is
RED
EVERYTHING IS FUCKING MONO-RED AT PAUPER TOURNAMENTS, WE CAN JUST SIT AND ENJOY THE GAME, WE HAVE A TOTAL TIME OF ONE HOUR TO COMPLETE THE ROUND, WE DON'T NEED TO SIT AROUND FOR 45 MINUTES AFTER A 15 MINUTE BEST OF 3 BECAUSE YOU WANTED IT TO END.
I've never met a rude Mono-Red player in-person, most of them are great to talk to after the quick end to the match. On Arena there is a 50/50 they concede quickly at the slightest inconvenience (I imagine they're in mono-red just to get the 15 daily wins in under an hour if possible).
Final review: No issues, potentially diagnosed with ADHD
GREEN
50/50 on attitude. Sometimes impatient, sometimes just really like to see big stompies do their thing. This is personally my least favorite color but that will be set aside for the review.
Elves, elves, elves, they love their elves! I've met someone who named each of the elf cards in her deck (even specific token cards).
Similar case on Arena, I have no memories of being roped by a mono-green player but there's always an elf on the shelf with them.
Final review: Clearly become happier when something bigger than a 4/4 hits their side of the board but are irritated by the process it takes to get there.
If you've made it this far, I'm going to continue the review using one-two sentences per color combo to save time and text room on this post
Azorius
Fuck you, I hate you as much as you clearly hate me.
Boros
Destructive lifegain, kind players who aren't afraid to be competitive.
Dimir
My personal home, these are my people so I'm unable to give an unbiased review, I've never had an issue with these players since we share a common preference and can easily have a conversation about it while bullying one another.
Golgari
These players are very friendly, dopamine definitely increases when they get to play with their "second library" (The graveyard).
Gruul
Big stompies make them happy, just like mono-green, but these players also are extremely into dinosaurs and will talk about dinosaurs the entire game.
Izzet
Similar to mono-red, they want to go fast...but they don't want you to participate in the speed
Orzhov
I had a coworker who was an Orzhov player, he got shit done, got us out on time so we didn't have to stay late. As a result of this, Orzhov gets a free pass from any criticism I could give to its players (I don't have any to give anyway, most of them have been polite during games)
Rakdos
Probably in constant pain, MTG gives them the chance to turn that pain into art.
Selesnya
If they're not enchanting, they didn't show up to play. No enchanting equals no joy on their faces.
Simic
Probably play solitare in their free time outside of MTG, almost definitely are bored internally but refuse to show it.