I would suggest you both of Brand Name and site functionality as branding is so important these days due to search engines as for instance when u search gambling is faster to get "gambling.com" site rather than other non named such.
Same thing for functionality as the more you have the more appreciation and enthusiasm some new gambler will have to join your gambling site.
For SEO then its relevant on having that in related with the business but we do all know that not all names that we do prefer or we do have in mind would be available and some of them are way too expensive
thats why they do end up on a name which arent that catchy but it wont really be that an issue yet everything could really be shown off or something that talks about exposure via those aggressive marketing.
People would eventually able to find out your sites existence even though the name isnt really that catchy or too famous to hear off but marketing would do the trick.
Functionality would be crucial yet this would be the bloodline of your business.