Any alt coin suggestion expect ada.In my point of view of ada still can't surpass ETH in the smart contract field and even if they can make it will be hard to be replace existing eth smart contract eco system.Moreover late coming project like sol even surpassing to ada,all things ada have is the loyal user base and nothing special things in tech
Don't expect ADA to fulfill and meet all your expectations. Obviously, the most logical approach should be diversifying to some of the best coins and not just by sticking into one. ADA is one of the best coins on our portfolio but we should consider others too.
I suggest looking every day at the altcoin's daily volume then from there, pick some candidates. Do research on those specific coins and try to look at the community's pulse and feedback, if there's any. Then after a period of research, now decide what coins should be picked. I have my own list but it doesn't mean we can have the same result.