I'd go against the grain here and take the 106.
An £1100 Fiesta 1.25 will be a Mk4 or Mk5. Whilst the engine is good, they are all at an age where rust is a problem. I looked at loads of these about 12 months ago and they all had rust to a greater or lesser degree, and it can be an MOT failure. The 1.25's can start to burn oil at higher mileages and I would say it is a more complex engine than the 1.1 Peugeot - it has more electronic components on it and they can give strange problems. If you're not handy with the spanners, I'd avoid it.
I had a 1.1 Saxo (which is more or less the same as the 106) - albeit many years ago, as my first car. It was reliable and didn't kill me - although it tried once! You have to be careful with no weight in the back, because if you jump on the brakes at speed with a bit of steering on they will spin easily.
What I'd suggest you do is up the budget a bit and go for a Mk6 Fiesta. It'll probably be a 1.4 as they didn't fit the 1.25 until later, but they are an infinitely better car in every respect - any the don't (generally) rust.