You want the 1.9DCi engine for sure. It’s got 105bhp, loads of torque, is pretty reliable and cheap to run (as long as you don’t mind changing the EGR valve yourself), does 45+mpg at all times, and 55mpg on a run, and it makes a passable family car (and actually a very good bike carrying car with the seats removed).
The 1.4 is woefully underpowered for such a heavy car, with no redeeming features as such. The 1.6 still isn’t as good as the 1.9DCi. The older 1.9DTi’s are only 80bhp and though frugal, again struggle with a lack of grunt.
What is your budget dare I ask? I wouldn’t really consider a 1.4 unless it literally was only £250, looking on ebay now there’s a few half decent looking 1.9DCi’s for just under the £1k mark, and there’s a couple of very low milage immaculate cars for under £1500 from dealers.
Had a X Plate 1.9DCi Scenic Monaco (highest spec) that I bought as a very tatty stop gap car off a mate about 4 years ago. Ended up running it for about 3 months, and aside from it looking like a shed, it was ace! Sold it to get something smaller and lighter with the same engine in (Megane 5dr 1.9DCi on a Y Plate) and half the milage on it, which I then ran for 2 years and it was the most reliable car I’ve ever owned!