CX251, 255, 257 (mon, wed, fri) are run on 747s, 257 on other days is a A340, which doesn't even have first class and 253 varies between 777 and 747.
When on a 747 I select 3K or 2A if I'm by myself, I like the privacy of these rows, there is a wider isle space then 4 and has a feeling of open privacy.
When travelling with someone on a 747 I select row one, row 2 would be my second choice, and I simply wouldn't choose row 4 (if the choice was mine of course)
remember on a 747 the further into the nose you are the less interruptions you'll receive because the F/A's don't have to walk past you to get to any other passenger. but then on a 777 (only 2 rows) you want row two because the F galley is ahead of the seats so the only time they'll walk past you is if they're going to you (or to J).
so if it is a 777 and travelling alone 2A first choice, 1A second choice because this isle only serves these two seats so it's very private. if travelling with someone 2D
, K first choice then 1D and K.
D is in the center sharing isle access with K so you're right across from each other, but D doesn't have a window, my girlfriend doesn't care about that but my mum does, so if you both want a window then go for 1A and 2A. Now the risk that you run is you can only select 2A and K at the airport as they are reserved for baby bassinets (never had one on board) so you'll have to initially select another seat and hope for the best.
All a gamble, but all seats are amazing, hope this info isn't too confusing and that you enjoy your CX
F experience, it's an amazing product.