A lot of these answers seem somewhat misleading unfortunately.
Forget about getting a capture card. Practically every one has AGC. AGC is very similar to macrovision, except it's superimposed onto any video source. It's impossible to disable unless you use Linux and know your way around hacking drivers. Some cards on Windows have third party tools to disable AGC, but the quality is extremely questionable and they all seem to use scaling and sub-sampling.
Think your best choice is finding an external device like a Panasonic DMR DVD recorder (these have a very decent comb filter). If you could somehow find an external device with USB or firewire, I think this is your best bet.
I think 4:1:1 subsampling should be kept away. I think 4:2:0 is actually better. 4:2:0 is most compatible and least problematic with transcoding and quality loss. If you get a device with 4:2:0 chroma, make sure it oversamples before subsampling; these seem to give the least quality loss after subsampling, and might be considered transparent sometimes.
For a laserdisc player it's hard for me to answer. You could stick with a player that doesn't split the composite or audio signal. These will have a single composite and audio output, with no RF or additional svideo or second composite/audio outputs. These also have missing features like digital still mode on CLV discs, and probably more common as very simplistic industrial players. People may recommend something like the HLDX0 or similar, but these are very expensive and actually pass the composite video through various noise filtering and splitting stages; these players are so huge and expensive I think because splitting analog signals introduces immediate quality degradations, which these players supposedly avoid according to their owners.
Avoid scaling at all costs. You'll get scaling artifacts immediately which isn't usually noticeable. Instead of 4k output, you should stick with whatever native resolution your capture device uses (usually 720x480). Let your software or hardware scale later, instead of the encoding and capturing. Same thing with audio. If you capture audio, make sure it's bit perfect digital stereo (LD calls for 44050khz according to wiki). Analog audio should be captured at 192khz 32-bit float at least, and can be compressed later.
Laserdisc video is actually pure analog AFAICT. RF is passed to a custom modulator and cut-off filters, which send the result to a TBC. TBC produces the composite video which is an analog signal. The composite signal can be routed directly to a composite video jack, but almost every player will split this into UHF, comb filter with svideo, and/or secondary composite output. The only players that avoid that are like those I mentioned previously (LD-V4200 I believe is one, and with a strong signal, albeit with noise).
Laserdisc video quality is a love or hate thing IMO. The quality is actually very high and with a high end system can be considered better along with its sound, vs DVD. Only LD's that may seem inferior are widescreen, or those improperly mastered. Quality is basically 425 TVL always with good chroma. DVD by comparison is considered 525 TVL before MPEG2 compression. Unfortunately MPEG2 reduces DVD video quality considerably, and the only advantage DVD has in this situation is a pure digital path with consistent quality (no analog difficulties like noise and interference). MPEG2 reduces DVD TVL resolution to a variable of maybe 250 to 500 TVL lines at best with considerably less chroma by comparison. Mpeg2 quality greatly varies depending on the movie, and the movie length unfortunately. Only exceptions might be "Superbit" DVD releases which are very small in number. See a DVD and downscaled HD-TV source for resolution and chroma comparison here: [url]http://www.cornbread.org/FOTRCompare/[/url]
I hope I may have been of some help. I think your best bet may be an external device with firewire or usb. AGC is the biggest problem you'll have to avoid, especially with computer capture devices (USB, PCI, PCI-e, etc).