I’m far from being an expert, but as I’m learning, it depends on several factors such as the recipe, the amount of moisture in the curds, temperature, and the size of the mold. I had terrible results until I learned to properly cook and drain the curds before putting in the mold, my first few attempts ended up with the cheesecloth hopelessly embedded in the cheese and were impossible to unwrap without ruining the exterior. Once I hit on the right consistency and temperature for the curds and realized that pressing is really more about merging the curds together into a single mass and not so much about removing liquid it was like the difference between night and day for me. Rewrapping between pressings has also been very important for my good results.
For my cheddar type cheeses so far I seem to have good results with about 50 pounds for a final 24 hour pressing in my 4 inch mold. But there are several variables so I’d be surprised and skeptical if anybody claimed to have a single value that is best for all cheddar recipes and mold sizes. Every recipe I’ve followed so far has suggested pressing times and weights and I’ve generally been following those.
FYI, I’m using a simple prototype lever press I made from some scrap 1x2 boards I had lying around. I bought a couple bolts with wingnuts and drilled multiple holes to make it easy to adjust the amount of leverage and used a bathroom scale to calibrate each hole for 3 different weight positions, printed it in a table and taped it on the lever arm. It gives me a wide range of force from 10 pounds to about 55 pounds with a single gallon jug of water, and I can double that range by just adding another jug. I intend to make a prettier press with a few refinements born from my experiences using it, but it’s worked so well so far I haven’t gotten around to it yet. 
My molds are made from 4” and 6” Schedule 80 PVC pipe scrap I got for free from a local irrigation company. They were pretty dirty and scarred up, so I used a dremel tool to quickly grind/sand the exterior and trim the lengths to clean it up, scrubbed out the interior and drilled a nice pattern of drain holes. I “repurposed” a poly plastic food cutting board cut to size with drilled drain holes for the mold base, resting on a half inch ring of PVC the same diameter of the mold, which supports the base well by preventing bowing under the weight.
I already had the tools and wood and since the pipe was free my total press and mold cost was about $2 for the bolts and wingnuts. 
When I’m not using it I can just disassemble it by removing the bolts and it stores away in a closet as easily as a broom.
I decided to go with a lever press because it doesn’t require any special hardware and has virtually unlimited adjustability. It doesn’t rely on spring tension for the main force, so doesn’t need readjustment as the cheese compresses, and is just ridiculously simple to use in my opinion. Then again, I’ve never used another press, but I don’t see myself ever trying anything else either. I don’t have anything against any of the commercial presses out there, but I just don’t feel the need to pay much to make use of free gravity.
