The line6 is a great looper. This pedal is a must for me. But the dl4 delay modeler is kind of a piece of shit lol, I've literally bought at least 5 of them over the years bc the footswitches bust & I needed it. This time I bought an m9 & it's much higher quality so of you go line6 bight the bullet & spend the 400 on an m9, and in addition to the looper & every delay imaginable you also get a model of pretty much every cool effect that's been used in any famous song, which is pretty cool.
I've used most of these loopers mentioned & the reason I've come back to the line6 is because of the way they have the footswitches set up, with the Rec/overdub, play, play once & reverse/half speed. This is just the perfect setup IMO & for me its become second nature. Also the footswitches are smooth.
I bought a boss loop station a few years back & I hate the footswitches, they're not smooth so it's difficult to get the timing right. When you're looping, particularly with another player it's absolutely critical to get the timing exactly right, the slightest bit can fuck up the whole jam. I spent like 300 on it & less than a month later I was back buying another dl4.
& the other delay effects that come with it are great, I get all my delays from that one pedal. Throw an expression pedal on there & you can do all sorts of shit, like change the amount of repeats on the fly, LLRain style.
So I strongly suggest going line6, but definitely an m9, not a dl4. In addition to being a sick looper that works great with all the other effects it's the most bang for your buck you're gonna get.