it all depends on what you like lol, panthers are great in temperament. jacksons stay smaller and have those cute horns, carpets are small but their patterns are amazing, and veiled are grumpy little creatures who only tolerate you because you give them food... nah I'm kidding lol they don't tolerate us but for real, veileds for me personally are my favorite, ive tried a jacksons but theres something about veileds may it be their cute little faces or (mine is a grumpy old man) their temperament that just gets me going. but do what feels right for u!! its your commitment so it should be your choice
+1 for a Panther. I love my veiled but my panthers are a lot less grumpy. The care is similar so it's an easy transition. Not to mention @Matt Vanilla Gorilla has some available and he breeds his to be tolerant. You won't regret it.
I LOVE Jackson's but to have one you need to commit to keeping a higher humidity gradient with live plants, lower temperatures over all, more misting or dripping and for best results over night fogging. Even with all that, horns rule!
Well for me it was the fact that I had a veiled and wanted to experience another species. If you want something similar to veiled but different you can look into flapnecks. I thought about them since the care is the same and they are smaller.