Dear Pipo,
Before you make any decisions on what boat to buy, consider a few factors :
The F16 class is a newly emerging open formula class , currently updating their class rules after a year of development. The fact that this would happen was made clear at the beginning, when the class was first formed. The guys involved are doing an amazing job, there will always be differences of opinion, and this forum allows those opinions to be known. I, for one, do not own a F16 boat, my interest is in any 16ft cat that performs better than it`s design size leads one to believe it will, mostly in modern design lightweight 16ft cats.
If you read the old class rules which are currently being revised you will see that whoever dreamed this class up has done a lot of homework on performance equalisation, admittedly mostly theoretical & not fully tested yet, however it allows boats of very different designs to race on equal basis as long as their rated performances are similar, even taking crew weights into consideration. I think the idea is great, it allows sailors with different ideas on what is faster to experiment within the rules. Most of the boats are one-design with minor modifications ie standard Taipan with spinnaker being the only add-on. Sure a Taipan sailor can max his boat out to F16 specs but then he won`t be Taipan class compliant. This is no different in the F18 class - Hobie Tiger can be modified to race F18 but won`t comply with Hobie class rules. But he can sail a standard Tiger in F18. The same as F16.
I think what happened in this thread is a bit of a lack of understanding from outside observers like myself who were not aware of all the facts before making comment. I personally believe that the class should allow all boats that rate at a similar ISAF/Texel rating to race on equal terms, irrespective of how long/short/fat/thin a mast is. If they have equal ratings they should be closely matched in performance. The alternative is to tighten up the rules so that all the boats are identical, then we`re back to one-design or worse still, one-manufacturer classes.
Don`t forget that F16, like F18 is made up of (mostly) one-design boats like Taipan, Stealth, Spitfire etc, so if you owned one of these boats you could race in your own class events AND in open regattas against F18`s & F16`s on an equal basis. I can think of nothing more rewarding than sailing a 16footer faster than a F18 !
Another factor to consider is your intended crew weight - If you & your crew are 2 big heavy strong guys F18 may suit you better, F16 allows lighter crews to compete - father & son teams, husband & wife teams etc. If your wife weighs 80kg+ & can handle a F18 spinnaker in 20knots then that`s your route to go - If she`s 55kg then F16 will suit her better. Do you intend to ever sail single-handed ? This puts F16 forward as the better option than F18.
All things considered both classes are amazing, however one will suit your personal needs better than the other - that`s what should influence your decision. All other arguments should be settled on the race-course !

Happy sailing.
Steve