im not sure, after being in both cars, and considering ive got a clio id say a clio!
the twinport sxi has got 79/80bhp whereas a clio 16v has 75, but i think the clio is a sportier car, vauxhalls seem boring in a way, they dont react very well, whereas my clio feels nice and twitchy and goes where i point it, even with a fair bit of body roll!
but then again,on the topic of speed, they are both small 1.2's, so whether one is half a second faster to 60 or whatever, its a little car thats ideal as a first car, and they are never going to be fast, so go with the one you will be happiest to get in and out of for however long you will have it....
it depends on your driving style and preferences, i find the clio interior much nicer, especially the seats, and i think they are a lot tidyer on the outside, but its all personal preference to the driver. the only think i prefer on a vauxhall is the standard sound system, as the speakers are better quality, but at the end of the day throw £60 at it and the speakers are replaced!
your mums right! a 1.2 is fine, just the 1.4 offers that extra bit that you always want!!!