well the flashforge build size is not as small as it sounds.
And you'll probably be mostly making stuff that fits in it.

Dual extrusion is a right pita. It either takes 3 times as long as you need wiping walls or you don't use the walls and get bits of the two filaments mixed in with the other filament.

It does depend on whether or not you intend to design/make stuff that needs a lot of support.
I pretty much don't design things that need support. But you might.

The ultimaker is faster, and a second head can be fitted - pretty sure they do an expansion kit. So if you've got the dosh - I'd go for the ultimaker, at the end of the day it's the better printer. And like I said pretty sure you can add a second head if you need to.

If you look at the print head you'll see that it's on the left hand side, leaving a big gap on the right for a second head.