As someone who has never owned a "pet" Sun Conure but who bred them for about 6 years and who owned 2 breeding-pairs of them (so 4 of them), and someone who does own a male Green Cheek Conure as a pet, I can tell you that the Sun Conures are loud...VERY, VERY LOUD! And the problem that most people in your situation is that not only are Sun Conures extremely loud, but they are in-fact extremely vocal parrots, and they actually do in-fact make noise/sounds/talking/squawking/screaming all day long, every day...
***Conures in-general are fantastic companion parrots, as pretty much all of them are known to be "Velcro-Birds", meaning they bond very closely with their person and are extremely loving, want attention and cuddles all the time, and want to be with their person all the time. That's exactly how my Green Cheek Conure is, he's a little love-bug who sticks to me like glue...But I've gotta say that even he is pretty loud, but not only loud, but also extremely vocal throughout the day, all day long. Constant talking, chirping, singing, screaming, etc. all day long...As I'm typing this I'm listening to him in the other room screaming away with my Quaker Parrot, another parrot who you definitely do not want if noise is an issue, lol...
Even if you are living in a newer Townhouse with thick walls and good insulation, if you have neighbors on both sides of your home, right on the other side of the walls, then I would have to say that either a Sun Conure or a Jenday Conure (extremely similar species of Conures) would not be a good choice for you unfortunately. They are great little birds and they are awesome, loving companions, but they are LOUD and constantly so...And as a former parrot breeder of over 20 years (and a car salesperson for almost 15 years), I'll be the first to admit that listenting to a breeder when you ask them questions like this one, any questions that could result in you not buying a bird from them, you need to do exactly what you're doing, go and ask the questions to experienced bird owners who have no reason at all to lie to you or to paint a very rosey picture for you...Of course the breeder is going to tell you that they "Don't really scream" etc...They want to sell you a bird...Kind of like "They're all the same color on the inside" and "You can't see the color when you're driving it" kind of a thing...lol.
***What exactly are you looking for in the new bird you bring into your life and your family? You've already owned a Cockatiel long-term, so you know what they are like, but what is it that you liked about your Cockatiel, and what is it that you didn't like about your Cockatiel? If you can describe the type of personlity, attitude, etc. that you're looking for in your next bird, and the type of relationship you hope to have with your new bird, we can certainly offer you suggestions on parrot species that you should research and go and spend time with, and that would work for someone living in a Townhouse...
Unfortunately I'll say it again, in your living situation with your neighbors, a Sun Conure is probably not a good choice at all, nor is a Jenday Conure...What you don't want to have happen is to go and bring home a new hand-raised, baby Sun/Jenday Conure, fall in love with it and bond with it closely, and then be forced to re-home it after a period of time because of noise-complaints. I have been working at an Avian Rescue for over 8 years now, and one of the #1 reasons why people re-home their pet parrots/birds is because they live in either an apartment or townhouse and there were too many noise-complaints by their neighbors, and they were put into a situation where they had no choice but to either re-home/surrender their bird or to move-out. It's a horrible situation to be in, and I've seen so many people and families (with young children crying their eyes out) bringing in their pet birds for surrender, only because of the noise complaints...And I'd be lying or holding back on you if I didn't tell you that many of the surrenders due to noise issues are Sun and Jenday Conures...
So better to figure out what species of parrot will and won't work now so you don't have to go through that horribly painful situation down the road...There are a lot of great parrot species that are just as loving, intelligent, cuddly, etc. as a Sun/Jenday Conure and that are also much more quiet and perfect for apartment/townhouse living where noise is an issue...Off the top of my head I immediately think of my Senegal Parrot, Kane. I brought him home as an 11 week-old, hand-raised baby from his breeder, and he just turned 2 this past September. He's just a little cuddlebug, he's loving, extremely intelligent, he talks, and most important to me is that he just wants to be with me all the time, and loves nothing more than to just spend his day playing with me, napping on me, cuddling and watching a movie with me, doing puzzles with me, and going as often as he can (when the weather is good) on car-rides and then shopping with me on his Aviator Harness...He comes grocery shopping with me all the time, he loves to ride around on the cart, he loves going for walks, hikes in the woods, bike rides on my shoulder, etc. And the Poicephalus Parrots in-general are a very quiet family of parrots.