Best and fastest don't usually go together! For a rose you might choose a repeat flowering rambler - have a look at the David Austin website for the size and colour you like (they don't all grow to the same height)There are lots of other climbing roses that will flower longer than ramblers too so do have a good browse through the catalogues as its such a personal choice.Ones with smaller flowers are often better than big blowsy ones on an arch. For the clematis remember that if you get one that flowers later in the season you will have to prune out most of last years growth every spring, which might be difficult when its all mixed up with the rose so an early one like Nelly Moser might suit you.