For me it is a matter of two things:
- Price tradeoff with economy (which is a function of how busy economy is vs premium economy)
- What seats are available in economy.

I agree with the two previous posters that if the front exit row seats are available to book in economy (I've had them before) then I'd work out whether the price difference is worth some width, a bit more recline and significantly better catering. For the legroom would no longer be an issue.

I like the Spaceseats now, for privacy, legroom, width and the higher standard of catering is a nice touch. However, let's not pretend that it is a significantly better position to sleep in compared with exit row in economy. Double the recline of a minor recline, in the sloping forward position with a beanbag under your feet is a small improvement.

So in short, if economy is cheap and I could get exit row seats, I'd go economy. If exit row seats were not available and the gap in price was closer, then I'd go premium economy. My default preference is premium economy, but I'd go economy if the price/availability is right.