Definitely bandlab. I am an absolute fan and dedicated user. Bonus you can download Cakewalk by Bandlab 64bit for free. (Previously sonar platinum)
Just an irritation note. Them crazee wrappers keep on nagging you to like their songs consisting mostly of F bombs and shaking someones booty. Besides that, many usable real instrument and midi loops.
Linkable for sharing and added bonus non GT peeps can also listen and like your creations.
Allows collaborations through forking or creation of a band with fellow users. Be warned, heavy on cell data but light on wifi over PC