How to resolve a compound DOMAIN name?

I was looking for a domain that has a format like this:

bestX/X(something else).com (20 characters dot com included, the "/" is not included I just used to separate the 2 words)
like 2 things in one, they are releated words.

Should I use the 2 things one after the other? or its better something like this?

bestXandX.com (23 characters dot com included)
which I think it makes it too long but maybe it's just my perception.

Or there is another proper way to resolve it?

Never really went beyond two word domains no matter how hard it got and made sure my main keyword is one of those two keywords.

I have seen a few people rank good with longer domain names but i think it may require more work

Looking forward to more opinions