ATCO 17... If you have good enough GPS coverage for your airfield then GPS is the way to go to get GOOD instrument coverage into your airport for folks who are GPS equipped. It is dirt cheap for the airfield too other than to have the appropriate instrument markings on the runway as well as having the appropriate field lighting.
A GPS approach will give you normal non precision minimums into the airport and you can make it pretty much however you want to go around other airports or obstacles, or you can go with the standard T arrangement as we use here. If you go with WAAS then you can get the GPS approach down to almost cat 1 ILS minimums 250/.5 mile and it will give you both course guidance and vertical guidance. It is quite nice. The only kicker to all of this is that you must have an approach rated GPS in the aircraft, but again for the airfield that is NO cost and only to that of the pilot. In the US we are getting more and more aircraft so equipped, in fact most of the new aircraft coming off the assemly lines are coming with IFR WAAS GPS's as standard equipment in an IFR package.
AOPA has this to say on their web site...
http://www.aopa.org/whatsnew/air_traffic/waas.html
If you have any further questions please feel free to ask. As to the TLS, NATCA has looked at it for the last few years and has been less than impressed with it. You can contact NATCA for how they feel about it...
regards
Scott