Ive had both a 306 Rallye and a 306 GTi-6, as well as a Clio Cup... so Im in quite a good position to comment...
Went from a 306 Rallye, to a Clio Cup, to a Civic Type-R and now back to a 306 GTi-6, as you can probably tell by owing 2 306s I like them! Needed to get a cheaper car for a while, so was looking for something cheap to run for a while that was still fun, and I picked up my current 306 for under £3k and its a cracker too, not an old shed!
The 172 will be a little quicker in a straight line, the Rallyes quite close to the mk2 172 in fact, the GTi-6 a little further off, but reallistically theres not much between all 3 once on the move. If anything the 306 is stronger at higher speeds due to the 6 speed box, but the longer 1st & 2nd gear hamper is slighty off the line.
To drive the Clio "feels" quicker, this is due to it being smaller, lighter, closer gearing (initially) and theres a quite a definate change at 5000rpm when the power comes in. The 306 is a wider power band, feels very torquey and is a different delivery. Initially quite long on the gearing, once in 3rd it gets very close and you keep going & going.
Handling wise, the 172 is very good, but the 306 is even better, really communicative steering, very controlable on the limit and has passive rear steering, theyre a joy to drive. I went from a CTR back to a cheap P-Reg GTi-6 and the 306 knocks spots off the Civic in terms of driver reward!
The build quaility although not like a Jap or German motor is better than my Clio was, in fact this 8 year old GTi-6 is more reliable than my brand new Cup was!?
Specs are pretty similar, leather & alcantara, electrics, climate, rain sensing wipers, ABS, PAS, alarm & immobiliser, CD player, etc... the mk2 172 has a few extra toys, like Xenons or ESP (later cars), so you dont get quite as much in the Pug, but it has got 6 gears!
Someone mentioned fuel economy above, and yes they are worse than the Clio on juice, its an older engine design, no tricks like VVT to help out there, and its also a larger heavier car than the Clio, however I average mid/upper 20s going to work & back, not hanging around, and can get 37mpg on a motorway run, so theyre not that bad.
The 306 is a class above the Clio in size terms though, its a bigger car, so more room and can seat adults in the back comfortably, not squashed in there, plus has a massive boot.
My current one is the rarer Phase 1 (old shape) GTi-6 which has less toys than the newer shape cars and weighs less, in fact its pratically the same weight as the Rallye but with some of the toys. Not got aircon, only a drivers airbag, no auto wipers, etc... but I aint bothered about this. Goes well though, needs a few bits of jobs here & there to get it A1 but Ive had it nearly 5 months now and loving it.
If you can find a mint late model GTi-6 with good miles, FSH and standard(ish) then you wont regret it... but, you wont regret buying a 172 either...
Id take a trip over to
http://www.306gti6.comwww.306gti6.com for their opinions as naturally a Clio forum will tend to favour the Clio and the 306 forum will tend to favour the 306, so hear both sides of the story.
The other thing Id recommend is to look at & drive both of them...
