We've got both, a GT for me and a 147 for the missus, both with 16v diesel and both mapped to about 170hp. The GT is prettier and turns heads. The 147 has, for us, more comfortable but less grippy seats, a better ride over bumpy country roads, and maybe not such good handling near the limit but we hardly ever go there.
We choose the GT for long motorway journeys, but the 147 for cross country roads. Funnily enough, the GT appears to use slightly less fuel, averaging 48 and easily doing 51 on a long run, while the 147 averages 45, maybe because it does more short journeys.
Both equally reliable, needing egr valve replacement, the GT bust a turbo pipe and a door handle but otherwise ok.
In summary, the GT is more special, the 147 more sensible. It's horses for courses.