Does "argumentative" have negative connotation? If so, what's a more neutral word?
Sadly though, the primary definition of (at least the adjective form) argumentative (ODO),
1 Given to arguing:
an argumentative child
and worse still,
This is not the same as being argumentative, or arguing just for the sake of arguing.
Towards the end of my little encounter with Sophie Ward we argue about whether or not she is argumentative.
is clearly negative sounding, the last two examples suggesting argumentative = 'arguing just for the sake of arguing.'
That said, there's also the secondary definition,
2 Using or characterized by systematic reasoning:
the highest standards of argumentative rigour.
The paper then directed all of year 10 to select one question, answer it and discuss the reasons for their answer in an argumentative 1essay.
If we have spent several class periods introducing conventions of reasoned evidence in argumentative 2writing, we usually look for such features in student papers.
Therefore, it is context and careful structuring of the sentence that will determine if the author intends to convey a negative connotation. Devoid of a clear contextual support, the connotation is naturally seen as negative, because of its primary definition and because of its relatively more frequent use in a negative sense.
Do use argumentative, with a clear context in support of a neutral connotation (Examples marked 1, 2 above may help).
Many years ago while working as a supervisor in a fund-raising effort on behalf of a symphony orchestra, I supervised a difficult employee who misunderstood me when I used the word argument. He automatically thought I was accusing him of being argumentative, when in fact I was using the term to describe a line of reasoning he was using. His failure to understand me took me by surprise, and my inadequate ad hoc explanation of how I was using the term resulted in my failure to communicate.
There is no doubt that argument can have both a negative denotation and connotation, as in the following uses of the word:
An argument broke out over whose turn it was to pay for lunch.
Or,
Why must you turn every discussion into an argument?
Clearly, the word as used above denotes and connotes a bit of unpleasantness, complete with bickering, yelling, accusations flying back and forth, and more.
On the other hand, the word can have a neutral denotation and connotation, as in the following uses of the word:
The debater's argument was well crafted and supported with logic, persuasive statistics, and a memorable closing sentence.
Or,
Jim's argument concerning what caused the accident failed to persuade the jurors of the defendant's guilt.
Clearly, the word as used above denotes and connotes a line of reasoning which depends more on a thought process than a verbal free-for-all.
Now the word debate can also denote and connote something positive or negative, depending on how it is used. Which of the following uses of debate is primarily positive, and which is negative?
The university's representative in the competition was clearly well trained in the art of debate.
[A mother to her young son] Why must everything I ask you to do turn into a debate?
If you think the first use is positive and the second is negative, I'd agree with you. The former use brings to mind a reasoned, rational, even impassioned argument in the context of the give and take of verbal sparring. The latter brings to mind a stubborn child who finds it difficult simply to do as he is told, without complaining, whining, resisting, and finagling his way out of obeying his mother.
As for a synonymous substitute, I suggest the following, the first group of which lean more towards a negative connotation, while the second group leans more toward a positive connotation:
NEGATIVE
distrustful
cynical
calculating
contrary
irresolute (the product of a failure to come to a conclusion--the "on the one hand, but on the other hand" kind of thinking which is never truly resolved in one's mind, one way or the other)
indecisive
opinionated
rationalization
clustering (amassing proofs in one's mind as to why a decision is--or was--a good one)
POSITIVE
skeptical (your suggestion)
questioning
reasoned
sensible
balanced and fair minded
balanced
reflective (tending automatically to reason things out in one's mind before acting)
to weigh in one's mind
rumination (mentally "chewing the cud")
incredulity (n.); incredulous (adj.)
In conclusion, to argue one's point of view could involve some negative and unpleasant interactions, but not necessarily. Similarly, a debate could be characterized by a complete lack of regard for the "rules of the game," rife with snipes, ad hominems, unfounded accusations, and made-up facts. On the other hand, a debate could be reasoned, rational, respectful, and fair; in short, it could take the high road, so to speak, and not the low road of insults, invective, and impromptu inveighing against an "opponent."
How about "counterargumentative"? While it is ad-hoc from counterargument (typically used in the context of reasoned debate), since you want something informal, that might be desirable.
A more formal term would be rhetorician:
rhetorician
noun
an expert in formal rhetoric.
Edit:
After reading and thinking about this a bit more, I think the connotation really starts to come down to your ideology. In one such philosophy, known as Sophism, students learned to dispute their opponent no matter what, using an "eristic" argument. Plato and others were staunchly opposed to this methodology, and instead preferred the "dialectic". That full discussion is likely out of the scope of the question though. In any case, I'd like to add "dialectical", from my point of view.
dialectical
adjective
1. relating to the logical discussion of ideas and opinions.
2. concerned with or acting through opposing forces.
Edit:
You might also simply describe yourself as a debater.