No accent is better than another.
I think being able to understand accents and identify them will help in the long-run though.
The accent you pick is the accent you like because it’s your personal style. As someone learning Spanish as a second language, you probably won’t get a “true” accent from either. I speak Spanish with a slight Spanish [Andalusia, Spain] accent, but I also have an American accent above all of that.
If your goal is to deal primarily with Spain in the long-run, then maybe one of Spain’s accents are for you. And if you plan on dealing with Latin America, they have lots of accents.
Because naturally occurring accents depend on region, you might not sound totally authentic. I can fake an English accent, but I’m not English.
I think it’s hard to answer primarily because of two reasons.
First, every country has multiple accents, so even if you focus on Spain’s accent, you’d still have to go deeper - do you want Madrid-style, Barcelona’s, Andalusian, Galician, Asturian, Extremaduran etc. The Catalonia accent is different from Castile’s which is different from Andalusia, though it’s still Spanish.
Which makes Latin America even more confusing since it’s multiple countries. Mexico sounds different from Argentina, and so on. And even in Argentina, the Buenos Aires accent sounds different from the Pampas accent.
Different cities or regions in a particular country tend to have their own accents, even if they all fall under the umbrella term of “Spanish” or “English” or “German” etc.
Second, most people pick up their accent depending on who they emulate. Most of my teachers were from Spain, so I picked up on their accent a bit. But if you have teachers from various other places, you might pick up their accent. In addition to that, the media helps influence your accent as well, especially for younger kids and for people who are emulating speech. If all you ever heard was the Southern drawl from the U.S., you’d probably speak that way because you wouldn’t know better.
You know you better than I know you. So whatever accent you gravitate towards is the one you like, the one you’re good at, or the one that feels natural. That’s your own style.
The only reason your accent would matter is if you’re after a radio or TV job, where you might get instructed on elocution or “radio speech” which is a neutral accent to appeal to lots of people. Sometimes people have their own accent coaches.
Another problem is that not all speakers of the same language can understand each other. The Australian accent is sometimes way different from American English. And just like that, Spanish speakers sometimes have a hard time understanding what another Spanish speaker from somewhere else is saying.
I don’t think there’s anything wrong with anyone’s accent. When you’re learning one, it’s about personal style. And anyone who believes that a certain accent makes you sound less credible or less intelligent isn’t someone you want to be around ever.