Compartment 06
After making sure his sister would be in a good compartment in the company of other first years she's already familiar with (and therefore hailing from approved families), Greg went to Draco's compartment. Yes, his dad is not so fond of the Malfoys right now, but this is what Greg has always done, and you never know if they recover from their current negative light.
Greg would find Draco's quietness a bit disconcerting (though obviously that wouldn't be the word he'd use to describe it) but for the most part he'll just leave the other boy alone and stick to reading comic books, eating and chatting with anyone else who might also be there. Occasionally, he'll get up and check on Gertie, but will come back quickly.