In the start of learning a new language one or the other may be easier for you. But if you stick to it long enough, it will come to a point that you have to merge both anyhow to be genuinely fluent so it doesn't make much of a difference.
Learning grammar and using it fluently are to very different things. You have to get to the point that you're not worried about the grammar--it just need to flow, and that can be difficult for any learner, AS or NT, who had been relying on learning grammar up tot hat point. I grasp grammar concepts faster than learning lots of vocab. But it's pretty much an equal challenge to use both grammar and vocab fluently.
I'm roughly fluent in 3 languages, have studied/am studying a number of others at varies degrees of seriousness. When I was younger, I took German in school. In the first 2 years I was way ahead my classmates. But the third we were even, in terms of using what we'd learned fluently. generally find this to be my pattern--the basics I can acquire very quickly, but then I level out to a typical learning pace as I try to learn fluency.
There is a difference in learning spoken languages and non-spoken one. I'm studied three non-spoken ones--Latin, Biblical Hebrew and Ancient Greek. Basically it's studying grammar in a different language, with a lexicon nearby for the words you don't know. But with learning for fluency, you have to get away from relying on grammar as early as possible, getting in real speaking and listening experience, which for me is very challenging, being an Aspie and finding conversing so very coutnerintuitve. Strangely though, I often find it easier to start a conversation in a language other than my native tongue, possibly because I'm talking about practicing my language skills rather than "Oh god, I have to coe up with small talk".