I decided to do some comparisons of the silver holos I own since I recently picked up Gosh Holographic. The other ones I own are Nfu-Oh #60? (I think) and SH Nail Prisms Diamond.
The Nfu-Oh and Gosh ones are really close and look spectacular without a topcoat. Diamond is kinda old and doesn't dry very well. I think the age of the polish is why it came out more grey than silver. I'm not sure how old it is since I got it off of eBay.
Anyway onto the comparisons!
All without t/c unless noted.
Gosh Holographic
Gosh Holographic next to Nfu-Oh #60?

Gosh Holographic, Nfu-Oh #60?, SH NP Diamond

Gosh Holographic 4 coats with t/c




So you can see the holo

After one day of wear :(
Holos do really suck at staying put on your nails. It might have been the four coats too.
On to the comparisons...
One Coat
top-bottom: Gosh Holo, Nfu-Oh #60?, SH NP Diamond

two coats

three coats

4 coats!

As you can see, Gosh and Nfu-Oh start out real streaky but begin to come to a full application. They are really close and holo-y. I would go as far to say they are dupes *maybe?*
Diamond- not so much

All the same as above
pinky- Gosh holo has the t/c and it does lose it's luster

SH NP Diamond- 4 coats w/tc

please excuse that bump on my middle finger, my nails are in bad shape (peeling) and the holo picks it up


same as above, in full sun
Thanks for looking!