Obviously bass because you only have to play one note at a time usually.
Of course people are now going to link to absolutely amazing bass players on You Tube that make Steve Vai sound like a beginner.
I wouldn't say you can get good quickly on either. It's an instrument, put in the time or don't bother at all.
Saying that, learning a few chords on guitar is probably easier than learning to properly fret and finger-pick a bass.