I feel like he would have been a more functional person; he would probably be better at magic, he would be more confident, less awkward, and a bunch of other stuff that parents help with.

He wouldn't had suffered so much from his relatives (I mean uncle Algie was a bit infuriating and Augusta was a bit harsh too considering Neville already didn't have much self-esteem). He would've been better at magic, always had a fitting wand (until after the battle at the ministry he used his dad's old one, which he probably wasn't the true owner of). I think because he'd have two attentive parents his signs of magic wouldn't have been overlooked (he actually showed signs early on but very subtly). He'd still be the best of course oh and maybe Snape would've gotten an earful from Alice and Frank, once Neville told them how he treated their son.

His life could've been so much better. He would have grown up with loving parents. He could've done better in school. The reason he was bad at magic cause the wand he used wasn't actually his but in this case he would have to start with a brand new wand.

He’d live happier