depends on the character, his damage, and where he is going to end up. If you think he'll roll behind you and he's at high %, for example, I'd probably punish with an f-smash, or upsmash, if you think that would kill better at your position on the stage. If they are rolling away from you grab is usually your best option, unless maybe you think you can kill with a dash attack. If they are airdodging and you're on the ground, charge a smash attack to him them out of the airdodge. If you're in the air, wait for it to end, and upair. Spotdodges, again charge a smash or grab. If the character can be chaingrabbed, then maybe a grab is a better option, especially if it has guaranteed follow-ups.
Generally FD is yoshi's best neutral, and it comes down to preference after that. Pictochat isn't a bad CP, either, but my favorite CPs personally are FD castle siege and delfino. Of course different characters call for different stages, so use your best judgement.