My other half recently bought a 51 pre-reg Authentique 1.2. My mum recently bought an 04 registered Dynamique 1.2 16V.
I drive both quite a lot and would say that you may as well buy a Dynamique as they were only £500 more second hand when my other half was buying her Authentique. Thing is, the Authentique has all the stuff she wanted - and she didnt need alloys, sportier seats and so on. All the important stuff like airbags, ABS and electrics are standard!
Theres very little difference IMO between the 1.2 60bhp engine and the 75bhp 16V version. I have also driven the 1.4 - and think the differnece is a lot more noticeable.
Overall, both the cars handle and ride extremely well. They both just seem to leap over potholes and rough surfaces, where a lot of other cars just crash and jarr. Both appear well built beyond minor trim rattles.
Do look out for the new offers on the Dynamique. My parents could afford to pay cash - and cannily took an option where although you pay interest, the overall amount payable is still the list price. They then paid back the "loan" after one month and essentially got a brand new 1.2 Dynamique with air con, CC, sunroof and metallic paint for £8,000 (rather than £10,600).