From your experience, what do you think is the best website to obtain random keys?

None, its a gamble, you never truly win

random keys are not random at all... it's not a coincidence that all the "random" games are all highly bundled and been free at some point..
basically they collect games for 20cents or (for free) and sell as random and people think wow what a great deal a paid 1$ for a random key and the game is worth 30$, next thing you know that game was literally free last month or in 1$ tier with a bunch of games on humble/fanatical etc

I was like you once. Now I pretty much only buy games I'm at least most likely to play at one point. 'Random keys' is a horrible concept if you think about it.

ALL mystery/random key offers are bad offers.
You get only stuff that they can't sell a other way, that were free or bundled many times.

I don't really like gambling when buying games, I have bought bundles and what not where one of the keys is random but I simply won't go for a whole pack of unknown keys.
On the other hand I'll gladly gamble with my time when it doesn't cost me any money, so I'm all in on sites like lootboy... or SG for that matter.

They are all pretty bad, but i’d say Fanatical is the best of them all, however only when they have some kind of special promo where you can win a pack of games or cash as a special prize though.

My brother used to do this and tried to convince me to do it at one point before I discovered bundles, because he got some "great games" in them along with a "load of shite." Hahah! He's the one that pointed me toward certain grey market sites with bundles of random keys and I honestly didn't buy any. To this day, I have steered clear of grey market resellers and not unhappy with my decision. Haha!

Don't do it. Depending on who you're talking to, some will think they are a great deal, but only because they don't know much about the bundle market where you'll probably get a game you actually want at a similar price. It is better to pay a few euro for a bundle that contains a few somethings you might love, than to pay the same for a load of keys that you'll probably regret buying.

if you mean ones you buy and don't know what you got till bought then you do know then steamgrounds for sure

It's - albeit legit - a scam. The amount you pay for the keys before you get something decent, is how much you'd need to buy the game in a bundle, on sale, or even from a trader... plus an extra to get more games you actually want.

With that in mind, think about it - why the fuck would you spend $7 (USD) to get 10 random keys of games that:

1. Is likely free/heavily bundled, cheap, low ratings scraps
2. You likely won't really want even if it turns out decent
3. Is likely not worth the value you might think it's worth

You take that $7 and spend it on a game you really want during a sale/bundle if you value your money. If you're just addicted to gambling, then there are better forms of gambling than that that aren't based on RNG alone, I'd suggest that over these scams. :P

and yes u are correct. All random key offers from gray market sites like gamivo are 100% "scam" and the only site really that is legit and does them is like u already said fanatical, but even there u most likely will get a worse deal overall by buying them than by just buying their normal bundles, but if u really want to buy them then theirs are by far the best deal

Never bought any random keys, because for 1 euros / key, there many other way for getting good game (Fanatical bundle, Humble Choice [For people like me that have the 6$ coupon), ...).
But have used in the past Lootboy and Indiegala for free random keys, many crap games, but first there free and specially for Indiegala, there are quite fast to get (10-15 minutes for 2 free keys)
Best game get in Indiegala : Flatout Complete Bundle (4 Games) / Chroma Squad / Ignite ...
Best game get in Lootboy : Path of Giants / Shadows: Awakening / Pressure ...

in terms of actually wanted, none in terms of playability maybe 1 or 2 from lootboy (iron brigade, dungeons 3, oh my gore), got a random from fanatical that id actually play (rebel galaxy) only got 1 to hit my 10$ spend for free gift. in terms of CV its about 1;1 in my limited tests