They both look cool in black! There are lots of non-looks reasons to consider between phases...
I bought a ph1 RS because it was cheaper - to buy (older), to tax (old system, rather than emissions based), and very very slightly cheaper on fuel (lighter car, longer gearbox - but really depends how you drive).
Ph2 has advantages such as a better interior, and higher spec elsewhere, and the car will be newer in general.
If cost is a main concern, then MPG is not the only thing to think about (in fact over 10k miles it won't make more than 200 quid difference).
Think about depreciation (a more expensive car stands to lose more money every year), tax (the new system does not favour big engines!), and insurance (I'm an old fart so it doesn't cost me much, but 20 year olds seem to pay big bucks to insure a RS clio).
Just my 2p - ignore me if you like!