They are the same underpinnings as I am sure you are aware, however I have never looked at a 147 and gone wow, that is a thing of beauty..Its a bit ordinary for me, that said many people love them and would disagree strongly with my opinion and that is exactly as it should be, vive' la difference'
The world would be a boring place if we all loved the same things, if you are really 50/50 on it then as firstcaralfa says buy the best condition one you can find, this will likely mean a 147 as they are more plentiful and cheaper than the GT to buy, they will however cost much the same to run.
I think the GT interior is a bit nicer .
I couldn't agree less with the lard arse statement made earlier, I think the GT is gorgeous from every angle...one point worth making is no matter what you do with a 147 it will always be a ''hatchback'' more power just makes it a hot hatchback, I can see the attraction but I don't think the 147 has nearly the presence the GT has. it would line up with an ST, a 208 GT ,a Clio Rs 200 and be in the ''right company'' the GT would be Lining up with Audi TT's, Maserati 3200's and BMW 3 series...it's all together a more grown up car.
The GT just oozes class and Looks way more money than its worth, mine was parked between a GTV and Maserati 3200 at Brooklands and really did not look out of place..I personally don't think a 147 looks wise sits comfortably in that company...the GT is definitely more of a statement vehicle IMO.
here are a few pics of mine, yes it been lowered(properly) and the wheels have had a recent refurb, and lots of other ''little mods''..and its mapped with a hybrid turbo. but bugger all that.
just look at it objectively, it's gorgeous! people genuinely stare at this car, some trying to work out what it is, as they are not common at all and I often get comments from people asking what it is, and from those in the know what a nice example it is.
its practical with a HUGE boot and the rear seats are usable if a bit difficult to access for some of my older relatives or taller friends..Scotland and back regularly to see my mum, and I always arrive fresh as a daisy with no aches or pains.
but none of this really matters,because whichever you choose it will be the one YOU prefer...
and finally no offence to the 147 owners,I know they all feel as strongly about their cars as I do about mine..as it should be.
good luck with your purchase, you are in for a fun and engaging drive either way..