As with most other Pokemon games, I always tend to pick up the regional starter bird Pokemon, and Hoenn is no exception. I'd probably argue that, while it may not quite match up to the amount of times I've included a Pidgey on my team, Taillow is probably one of the Pokemon I've been the most consistent with keeping on my team. Only few times, which also includes my current playthrough of one of the games, have I not picked up a Taillow due to wanting to try something new, but generally, I feel like Taillow is probably one of the best starter birds to pick up next to Starly, when it comes to how much of an impact it'll make on your team. Most other starter birds are relatively weak just as you get them, but this isn't really the case with Taillow. Quite the contrary, I've always found it to be one of the strongest birds early on in the game, and while that may just be an illusion I've made due to the second gym being a Fighting type one, I've always felt like Taillow/Swellow just slaughter their way through everyone early on in the games. And it usually tends to keep it up up until around the 5th-6th gym, where it, unfortunately, starts to fall off; more so than most other starter birds I feel. I usually tend to keep it on my team, but it's usually not all that useful at that point, other than being a means to Fly.
But yeah, generally I've always really liked Taillow/Swellow, and often tend to overlevel it quite a bit early on, simply because it's so easy to do so, but the fact that it becomes so weak later on in the game does at times make it tempting to replace it, but I couldn't do that </3 But yeah, it's definitely the Pokemon I've had on most of my Hoenn teams :D