I would say it depends on how much you want to spend, whether you prefer one look or the other, and the spec you want.
From my own recent (December) purchase of a Mk2 Cupra R, when comparing the 3 - Cupra,
K1 and LCR , as has already been said, a remap takes all 3 to the same power.
The genuine
K1's only seem to differ from Cupra's with the bodykit and exhaust (plus any of the few options the original owner specced), but seem to command quite a price premium compared with a Cupra or a Cupra with the BTCC Kit.
The LCR on the other hand was a run out model of the Mk2 with Full Diamond Stitched Leather Interior, Hard Backed Seats with a Gloss Black Finish, Xenons with AFL (xenons were only standard, I believe, at certain times in the Cupra's lifespan and optional at others), the power increase you already know about, and an Electronic Diff (XDS).
Most (but definitely not all) then seemed to have the Tech Pack, which adds Front PDC,Sat Nav with DAB and Bluetooth, you may find one with a sunroof, but that seems rare on any Leon, and I think there was another "Pack" but I don't know what this included.
Because it was a run out model, thus at the end of the model cycle, it is obviously newer, and therefore more expensive than either of the others potentially.
Most LCR's seem to be 14k+,
K1's 10-12k but Cupra's from as low as 6k, all mileage dependent obviously.
As for the LCR, if your budget will stretch, I would definitely recommend one, but I am biased afterall.