JetBlue has 32" - 33" of space in Economy depending on refit status and ~38" in Even More Space. Delta has 31" to 32" in Main Cabin and 34" in Comfort+ (on their A321s).
Now that jetBlue has an interline partnership with AA, they should deal with IROPS better, but you might end up flying AA.
Is it a true interline partnership in that in my B6 flight gets cancelled, I can get put on an AA flight without issue?