Some interesting approaches. I am primarily a guitar/bass player but I can muddle my way through on a keyboard enough to get a chord/melody struture together. For me it really depends what I'm trying to write. I usually open a project in Splat with EZ Drummer open and pull up a pattern that's close to the feel I'm looking for and start banging away on the guitar/piano in loop/comp mode till I get a couple of things happening that I like. Anderton had a good tip about dragging some takes over to the browser then dragging them back into a fresh track to assemble a rough draft/arrangement which I find very useful. Or..
I open Maschine Micro in standalone mode if it's more of a loop based feel I'm going for. Get some patterns and sounds/arrangments together and then bring it into Sonar. Or..
Run Splat with VIP/ Komplete Kontrol open if I'm trying to do a Tension/Hybrid type thing and I'm just browsing through sounds to get a mood happening. I'll record to different tracks and start building from there.
Then again I might just sit down at the piano/guitar with a pen and paper and not go anywhere near a computer!
At the end of the day, it's all about whatever gets my creativity going. It all ends up in Splat at some point, which is just the medium that I prefer to use. I love hearing about the different ways people get their creativity on! Very inspiring!
Yours in Music,
Rip