I personally find metal nozzles best, if you have a TK Maxx near you they have some pretty decent sets in at the moment, including the Wilton cupcake decorating kit with the coveted 1M nozzle in it and some disposable piping bags for about £8.99. I picked up an unbranded piping set from there with a good bag, about 6 nozzles, flower nail, coupler and nozzle brush for £5.99 that came in its own case which I have found invaluable also.
Bags are quite a personal issue - I like both, and will quite happily use either.