SLMG licence first, definitely.
a) it will be cheaper & automatically come with a tailwheel rating
b) it's much easier to add a microlight rating to an SLMG licence than vice versa
c) come EASA (June 2012) your NPPL SLMG licence can be exchanged for an LAPL TMG licence to which you can add an SEP rating & ultimately upgrade to a full EASA PPL.
This place offers both SLMG & PPL training.
The microlight to PPL route is quite convoluted & will be completely impossible after June 2012.