I was thinking of getting a benchtop jointer as well. I have an old Craftsman 6 inch jointer. My motivation in exchanging tools is to save some space in my 1 car garage.

The advantage of my current jointer is that bed is a few inches longer than the benchtops and the fence is beefier. It turns out that I use the jointer a fair amount, so much so that a benchtop would always sit on the bench.

With a benchtop I'd have an enclosed jointer to run dust collection to and as it would most likely sit permanently on a rolling bench I'd gain a small amount of storage underneath it. 

I'm interested to see what other woodworkers say as well.

If I went benchtop, I'd likely go with a Rikon.

I'm in the market for a good quality benchtop jointer. 6" cutter should be fine for the kind of work I do. If  there is a strong argument for 8" I'm willing to listen. My priorities: sufficient power for most common hardwoods; low vibration; fully enclosed cabinet; reliable and stable adjustments to get dead-on 90 degrees; acceptable noise; 4" dust ports.

Your opinion: 2 blades vs helical vs spiral.

I'm prepared to buy a new machine, but will also consider a used one in good condition if you know one is available. 

I'd welcome your opinions and advice.