The 1.2 FIRE in the Panda has had at least three significant 'upgrades' since 2007.
There's the 60HP Euro4 engine, used in the ecoPanda until late 2010 - the main difference from the 2007 model is they run on thinner fully synthetic oil & ecotyres and just squeeze into the £30 band at 119g/km.
Then there's the 69HP Euro5 engine, used in the last of the Mk3's and, until recently, the Mk4. Higher compression ratio, vvt (for emissions, not power), and 6g/km less CO2 @ 113g/km in the Mk3 Panda (but still in the £30 tax band). This enabled Fiat to fit alloys to the last of the Mk3's, and still keep the £30 RFL. Downsides are the power band is higher up the rev range; lower down, where it matters most, it actually produces less power than the 60HP engine it replaced. Also it's no longer a fail-safe design, so regular cambelt changes are more important on this engine.
Current cars have the 69HP Euro6 engine; this appears to have a new interlink between the clutch and the engine ECU which has changed the way the car drives when pulling away - this is currently an issue for some, though not all, new owners.
IMO the 60HP Euro4 is the best of the lot; fail safe & better bottom end torque than the later revisions. Great economy, too; I've averaged over 55mpg in more than 50,000 miles of trouble-free motoring with this engine.