unless you get the 2.0 litre HGT bravo, any bravo engine will do better mpg than the 1.4, its a really poor engine design, that for a 1.4 doesn't get very good power, or good mpg.
I own one as well, and are annoyed that I happened to get one with that engine, but I'm happy enough because it's a bravo and where I live they are rare, and look awesome.
If you're going to get a different engined bravo, then I'd suggest the 1.2, 1.6 or the JTD.
The 1.2 gets good mpg, and is quite nippy, it can also be remapped for cheap, to give it a bit more power, cheap to insure etc. as well. The 1.6 has a good balance between economy and power, it's very quick for a 1.6 engine! Then there's the JTD is you like diesels, great mpg, good power, and can also be remapped to crazy limits of power.