I've been driving an ST a lot recently, great fun little car. Bit noisy on the motorway, 35ish mpg if you drive it carefully.
Only driven the Clio very breifly so can't really comment on that but the interior looks very tacky. Not that the STs is anything special but its definitely better than the Renault.
Very unforgiving if you drive it hard though, had a drash in one on a track last year, took a corner at 60 one lap, no problems. Went in at 61 maybe 62 the next lap and completley lost it - no warning you're on the edge until you're already over it... but maybe that was all down to my bad driving.