This game may be my all-time favourite piece of media. I would recommend it in a heartbeat, but definitely take the content warnings seriously — it can hit very hard sometimes. My recommendation for order of the routes (and luckily the order I managed to play them in) is Route 65 (technically a separate game) -> Leo -> Carl -> TJ -> Jenna -> Flynn if you'd like to maximise emotional damage. Spoilers ahead.
My first experience with Echo was actually Route 65 since my dumbass thought it was the actual game. I'm quite glad it worked out that way though since it set me up perfectly to head straight into Leo's route and ignore every possible red flag thrown my way. Naturally, I chose the bad ending first and it absolutely devastated me. Looking back, I should have seen it coming from a mile away. Leo's route honestly still hurts the most, though TJ's and Flynn's give it a good run for its money.
I next went through Carl's route and while it's definitely the weakest of all of them in my mind, it was still quite enjoyable. I can't laugh at any of the dumb decisions people make in horror movies now cause I went down the bad ending route first. Oops. I honestly thought James would do more damage if Carl resisted him. Overall, pretty good. I do wish Raven had more to do though :(
TJ's route was a return-to-form for the emotional devastation. I could see what was coming way before it ended but I was hoping to god that it wouldn't work out like that; the only thing keeping me going was the thought that the world might honestly be better because of Sydney's death; after all, he probably did kill his dad and was in the process of drowning TJ too so it's actually ok right? I think TJ's route hurt even more after that scene in Flynn's route. I didn't think that anything would be worse than seeing Sydney shoot his dad, and I was proven wrong. Absolutely incredible writing.
Of course the rest of Flynn's route was also awful; feeling helpless and being forced to condemn Flynn even though I knew the truth was really hard. Seeing the true nature of Socket Face made me reconsider everything else I'd already seen before. This game is really good at doing that honestly — so many parts of routes shed a whole new light on the others that really made me question myself. I should have seen that Leo wasn't the perfect wolf I wanted him to be all along; I shouldn't have been so quick to assume that Sydney was a horrible person (he's just a child, what the hell was I thinking?); I should have noticed that TJ was just awkward and not actually into Chase. The game is structured in just such a way that it's easy to fall into these assumptions so that when the carpet gets pulled from beneath you the ground hurts even harder.
Jenna's route was actually my second-to-last, not my last. Quite glad though; while Jenna's (good) ending is lovely and feel-good, Flynn's does a much better job of wrapping up the story as a whole. This route pairs very nicely with Leo's route; giving a lot more context to his and Chase's relationship as a whole. Realising that Chase had been messaging him still felt like a horrible betrayal, and also learning more about the details of their "breakup" with the phone prank helped me see Jenna in a new light. Previously I had assumed that she was kinda the best of them all. She got her life figured out after dealing with her trauma, and now in her route she's able to support the people around her, even the ones who wronged her in the past like Heather. Playing through the Phone short story and getting to see exactly what happened really tarnished that perfect image I had of her. The prank was in bad taste and definitely contributed to the extremely unhealthy relationship that Leo and Chase have during the main events of the game; it definitely feels like she encouraged the prank in order to sort of reveal to Chase that his relationship was not a very healthy one and to push him towards what she believed to be his best future (not to say that she's wrong, obviously their relationship is unhealthy, this just isn't the way to go about proving it). She does a similar thing when she yells at Carl during his route; while she may be right about the fact that Carl should stop being quite so much of a introverted stoner, this certainly isn't the best way of getting him there.
Anyways that's a lot of text. Overall, this game is an unforgettable masterpiece. I really hope you heeded the spoiler warning and aren't here without playing the game yet, but even if you are you should still play it for yourself; it's an amazing experience.