Old does not always mean good, we should not generalize it like that. We have seen there are still some old sites which cant be trusted. One of the site is 999dice, it is very old site but many people says agree that it is not a good site. Also we should not only judge which site is fake/scam, we should have valid proofs to judge a site is scam. Otherwise our judgement is just a baseless opinion.
I agree, what we should be looking are the old but reputable gambling sites, they are popular because they are reputable.
I would always trust the old once as long as they are legit, trying the new one is also good as they are surely gonna grow if they will continue to compete and will prove they can win in the competition, but that's not the best option for me.
Honestly, it's hard to find a reputable casino, so if you find one and you feel they already have the games of your satisfaction, you should maintain playing at that site, some gives always loyalty reward, so that's a plus factor if you are a loyal customer.