I think all dedicated loopers use automatic crossfade ! I prefer midi sync loopers.
I like Boss loopers, especially RC 505, sold for MKII version.
Really good to make 5 stereo loops with different lengths (up to 2GB recordings !) you can remix on the fly with track fx and faders.
Finally I bought a second hand RC500 for Syntakt reasons, and for a small guitar setup (with HX STOMP). I’ll see if it will match an OT+ST setup. I’d want OT master. I’d be able to record 2 longer loops with the RC500, with free length, other (mangled) loops with OT, matching pattern length.
Timestretch fluctuations with RC loopers if slaved. With RC500 I got freezes sending too much midi data for playback control, drums sequencing. Btw this is a good feature (possibility to sequence drums with notes), you can also find on RC 505 MKII.
Pigtronics, EHX, Aeros…