Depends very much on your budget Mark, if you can afford £200 then there are still some of the Irdeto cams around that can be or have been flashed to allcam or freecam, thus giving you Mediaguard and iredeto on the same cam.
If not then either of those two systems will give you a bundle of English language film channels
Irdeto series1 CAM flashed with FreeCAM2 v0.17 firmware, used in combination with a Funcard or "Silvercard" (piccard2) suitably programmed with Fun3-in-1 or DS9 (respectively) will give access to Irdeto/Betacrypt, Mediaguard ("seca") AND Viaccess.
er, at the moment. Who knows how lomg this bonanza will last. My guess is: not more than a few more months.
But I also want to point out that the question is a bit strange. The best way to approach this issue is to find out which channels are available (eg by referencing a site such as Lyngsat), then determine which are on your available sats and under which encryption system(s) they are broadcast. Only then can you make an informed choice. And it all, finally, depends on your taste of course (which you didin't tell us about). Sport? Adult? General entertainment? News? Film? etc etc. They come in varying quantities...