From these two, definitely the Butterfly. I mean, a 2 years old is already a larger toddler, and he's going to just get bigger. The Butterfly has a MUCH taller backrest and a longer le rest, so even without the full lie flat, your boy will nap more comfortably and will have more space overall to grow in.
Remember, though, that BOTH are ultracompacts for OCCASIONAL use, meaning not really made for cobblestones, terrain, nor everyday multi-hour use and naps. I personally would go here for a bit larger stroller, not a travel stroller which both are. People seem to forget that you don't need, want the smallest thing possible for everyday use - it's use will always be limited - by the small wheels, the narrower seat, the less sturdy frame... Just food for thought, I personally would rather go for comfort of a larger seat of a mid-site pushchair (e.g. Oyster Zero with a nice wide seat).