no doubt both the 156GTA & 147GTA share the same engine, basically the "same" platform and numerous othr similarities, EVEN SO, it shld be strongly noted tat BOTH the 156GTA & 147GTA still provide for a markedly different feel and overall drive...
"crashy" ride or what have u in a 156GTA i really cannot confirm - but very much believe it cld be sorted out wit a set of reasonable set of aftermarket suspension... Bilsteins etc..
i own a 147GTA meself and had the chance of driving me bud's 156GTA for a short time...
so the overall impression:
156GTA: surprisingly the ride is very refined (IMO and compared to me 147GTA on KW coilovers) and the engine note was more Ferrari like (higher pitch note) thereby it gave me more of the italian race car "feel". The owner fitted Koni adjustables on the front and Bilstein B8s on the rear wit stock springs

and the car still had a hug the road feel...(he is waiting for his bilsteins coilovers and is a dealer of sorts in suspension... so...

)
the gear shift seems somewat smoother in a 156 GTA too... dunno why tho... but certainly the car gave an overall more comfortable ride and still had the power to mak othrs !!!! in their pants...
147GTA: more of a wilder sibling of the 156GTA... more raw, very agile and chuckable WITH THE RIGHT SUSPENSION... very bassy exhaust - and a fun yet stylish car tat will certainly turn heads (156 GTA too..!).
i believe the different gear ratios & the chassis type contributes much to how both cars feel when on the road.. REGARDLESS, i gaurantee u tat the true potential of the STOCK 156GTA & 147GTA is not yet reached...
i wldnt exactly say which car is better than the othr cos they are suppose to serve slightly different target owners - but its a no doubt tat the 147GTA has more pizzaz and "get go" in it...
hope i didnt confuse u !!
cheers!