I've got a reasonable amount of experience since mine has been incrementally upgraded over the last 3 years.
"Best" way to go is an impossible thing to identify. It depends how much you want to spend, how dirty you want to get your hands, whether you want to take the cylinder head off and whether you want to rebuild the bottom end.
Leaving the existing Supersport cams in place and the head untouched you should see a moderate increase in power by switching to throttle bodies (and a programmable ECU). Not a particularly good performance increase per pound at this stage, but you will then have the 'right' bits for the next stage which would be to remove the cylinder head to have it reworked. I would recommend the Jenvey direct-to-head bodies and the Emerald ECU as being the most cost-effective solutions. I don't believe there is much point in changing the (Supersport) cams without reworking the cylinder head.
Or you can approach it from the other direction and get the head modified, leaving the plenum in place and putting the throttle bodies on the future upgrades list. This approach will also yield a reasonable power increase.
Getting the head modified and fitting TB's does put you in a position where a more extreme cam will yield useful gains, although to go much further than the Supersport cam you will need to junk the hydraulic tappets and get solid ones which are expensive (300-400ukp plus fitting/shimming) but are a good idea for track work (all the race cars use solid tappets irrespective of cam profile).
Once you get to 170+bhp you really need to think about replacing the pistons, which means a bottom end rebuild.
Hope this helps. Feel free to email me if you have questions etc.
Mike