Sorry, im still not buying this that they are comparable in price. Forgetting any negotiated discounts the 3 door GTI vanilla is £25,845 book value. The 3 door 135 is advertised at £30,555. That's still nearly a price differential of £5k which is not insignificant.
The figures quoted above where the cars are the "same" or "similar" in price (£32k for 135i and £33 for GTI) are for a cars with options and a large discount on the BMW and no discount on the GTI...

I think I can summaries this thread by saying:
- The 135i has better performance
- Whereas the GTI is more versatile
- The 135i is pretty cheap when you consider performance
- The GTI is pretty expensive when you consider performance
- If your budget is between £25 and £30 (i.e. you spec a GTI with a few options) then the GTI is several grand cheaper, which can easily be the difference between a sale or not
I've gone for the GTI and I'm paying quite a packet for it with the options. Yes I could get a 135i (with a few less options that I kinda would want) but do I really want to do that for 1-1.5 seconds faster to 60? In my case I will be very happy with the GTI performance, the history of the brand and the "can do anything" nature of the car... especially with a young family that I have to consider!
EDIT:
zerotosixty tells me that the 135i gets there in 4.8 which is 1.6 seconds faster than the GTI, but anecdotally the GTI can knock at least 0.4 off that... whatever.
Thats brutally fast for the BMW, but that alone won't sway me this time round.