Here's my opinion on the Nissan Cube for what it's worth- some people say that advice is only worth what you pay for it.
First, let me recommend that you look for a 2011, 2012, 2013, or 2014 model year Cube. (2009 & 2010 Cubes had known CVT issues; Nissan doubled the powertrain warranty to 120,000 miles or 10 years. I have read stories of 2009-2010 Cube owners having their CVT's replaced, some even 2 or 3 times.) I personally chose to avoid those early year models just to be safe, I don't have the money to take the chance. Nissan put new CVT's in 2011-2014 Cubes. I purchased a 2013 Cube S (CVT, not manual) with 23,000 miles, last march. I have very little knowledge about the manual transmissions, but I haven't heard any complaints about them. (somebody with knowledge of this may chip in) Due to commuting to work and taking road trips, I'm at 61,000 miles today. Even though that's nearly 40,000, the Cube still runs like new. I commute about 140 miles to work daily (Monday through Friday, 75% highway, 25% city) and would definitely recommend this car. I'm not sure what your daily commute looks like, but I can tell you that the Cube doesn't do too well in crosswinds. You will get blown around the road quite a bit; I get the occasional windy day here in upstate NY, but good tires seem to help that. Overall, it's not a deal breaker unless you live in an area that's prone to a lot of windy days. I have Goodyear all season tires on the car and have found them great for both summer and winter driving in the snow (not sure where you're located)
Secondly, I believe the CVT 2013 Cube gets around 27 city/31 highway (Manual: 25/30 MPG). I haven't ever measured what I actually get for MPG, but i'm probably nearly the 27/31. I'm a very relaxed driver, but driving through the Adirondack Mountains every day hurts my MPG a bit. I would expect the average MPG to be around 31/32- maybe a little better or worse depending on factors such as driving style, city vs. highway, etc.
Overall, I think you would be very pleased with the Cube. If possible- look for an "SL" model as they have a few more "perks" and upgrades. In my opinion, I prefer to drive a Cube with the CVT. There are a lot of great forum posts on this site, but not many "active" users anymore.