Hi,
If your'e loking for space, fabia will be slightly more roomy than polo. Polo backseat is not good for 6 footers especially the headroom. GC in polo also seems to be slightly lower but the car per se is more attractive to look at as compared to fabia. Features will be beneficial as you have to live with a car for a long time. So fabia being more feature rich will be a better choice along with the price. See if the features which the polo lack can be fitted aftermarket & at what cost. If yes & feasible cost wise then go for polo.
But both the engines make a lot of noise to be very frank. I had done a TD of fabia & during the drive I was almost in 2 minds if it was a diesel or what! Fabia had a terrific sound system I remember.
All in all, see what your priorities are do a complete TD & decide. BTW if reports are true FABIA SCOUT is around the corner too. check that out if you can wait...
Cheers
Jazzy