The clear hais vga box in the 2nd picture has my vote
with hands on experiance for that model I can confirm it is easy to use and does the job for vga and arcade use.
you can also open the case and clip 1 wire or the other and get them to display native 15K 25K and 31K
some of the others pictured I have not used but I have seen others make post where they had nothing but problems trying to get them to do 15K on arcade monitors.
The hais you just open the case and clip one wire and it's ready to rock.
The official DC vga cable is rare and costly and should not be hacked up in my opinion.
Some arcade monitors will require a video amp like ultimarc sell's some monitors are fine but some will require the extra voltage increase otherwise they have a dull/dim display.
if you want to run multiple console's like jamma PC DC etc.:
make your control panel wires run to a DB25 and you write each and every pin signal down to the T and do the same for your DC controllers and also the same for your jamma harness PC etc. then you can have all of them hooked up to a DB25 switchbox and be able to swap from DC PC jamma and what not without any tools or figuring out what wire goes where with the tangled mess of wire's in between type thing.
This way you want PC turn the knob and its done then you want to change to DC turn the knob again and then it is done etc. so much easier faster and cleaner in the end and it also make's it more convienent to add more console to it that way too.
if something acts up just unplug it and pull it out fix it and plug it back in just like you would on your xbox ps2 gamecube etc. no need to rewire the cab all over again becuase of terminal blocks or other means of manually playing around with wires & tools each and everytime & trying to figure out what one goes where type thing.
use DB15's for the video on a DB15 switchbox
here is a quik official pcb pinout I made real quik and will polish up later

Instead of plugging the stock 1/8" PC speakers stereo jack into the hais vga box I used one of these RadioShack Gold Series Audio Y-Adapter Instead.
http://www.radioshack.com/product/index.jsp?productId=2103710
That way your DC sound can now plug into your exsisting arcade sound amp and speakers or jamma setup through the RCA cables.
Me I have everything ran to a home theater surround sound system set instead of using the stock arcade speakers and amp or the over rated and over priced PC speaker sets I went with a real name brand surround sound home theater reciever and speaker set becuase of the rca style adaptor
Ok, I know this thread is old, but the info is still relevant. I know you can get the VGA box to output 15kh, but didn't know 24hz, and 31hz, well it does that natively, without any mods. So how would you get the VGA box to display 24hz? I understand it's pin 6, the blue wire you cut for 15hz, but how do you get 24hz? Is what has been said in the quite true and accurate and what are the benefits.The reason I ask is, I suspect the Dreamcast will look better at 24hz than 15hz, because is mid resolution, is this accurate. Would a game like Capcom VS Snk, with 3d background and 2 d player sprites look better than 15k, than 24k?The monitor I'm getting does both 15 and 24 is my understanding.Thanks for your help guys.I wouldn't be so close to finishing my arcade machine if it weren't with help from people on sites like this.