For a new Specialist coming out of basic, what kind of NCO should they seek guidance from to become an effective leader in the future?

I've found that you can learn from all NCOs. My advice:

1) look for newly promoted NCOs with a short time in service. They're hungry, they're fresh, they're motivated, they can get you promoted too.

2) seek out the guidance of senior NCOs. They've been around, they know the Army and have seen it change over time.

3) find the bad NCOs, they'll be easy to spot. Learn what not to do, how not to be.

4) start becoming a leader. Lead soldiers, so why you can to help encourage and motivate them.

Wow, is this the NEW Army. Didn't know you could "choose" you NCO's. LOL You will have to OBSERVE the NCO's to find one that not only "talks the talk" but "walks the walk". Be wary of those that say "do what I say, not as I do!"

If you are unable to "find" this type of NCO, then become one. This will attract others to you and the exchange of information can only be beneficial to all of you. Be the person that you would be proud to serve under and with.

Your a E4 promotable coming out of Basic training?
Either that is a typo or there is more backstory that would be needed to answer your question.
A: you dont really get to choose your NCO's you will be assigned 1st line supervisor , depending on your MOS, the unit make up and mission that may be a E4 team leader, a SSG Section leader, a WO1, 2, 3 department head, or a Federal civilian....
Now of the many leaders you will likley have direct of common contact with you may find one more willing to listen and advise, one that has like morals, ethics, work ethics as you, and appears at least to be successful in the job, unit, Army.

LISTEN .....choose apropret questions, relative to the job with answers you can not find yourself with even the smallest amount of work. If you think you know the answer better,,, Ask for confirmation after explaining the question, what your research found, your source.

It gets old answering questions a subordinate or peer could have easily figured our for them self... But Most leaders will happy help confirm what you already did the leg work on to learn for yourself.

First of all at that early point in your career you need to focus in your immediate supervisor. Once you learn the ropes in your unit you can begin to observe other NCO's within your unit. It is easiest to learn through observing, reaching out to NCO's extraneous from your section or team. You take the good attributes and traits that work with your personality and beging to add them to your personal kit bag. Watch and learn.

Welcome to the team! As you will have no doubt read, you don't get to choose your NCO's. However, you can choose how to respond to them. You will know if something is right or wrong in the time it is asked of you. For me, the ideal soldier is someone that is hungry to learn. So having a mentor that is hung ho, hungry for education and motivational goes a loooong way.

On a side note, I have a podcast with some basic stuff for new and aspiring NCO's. Who knows, maybe you will find some nuggets in there.
Podcast: sgtstime (can be found on iTunes)

Website: Sgtstime.weebly.com

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Once you get to your unit, your Team Leader and Squad Leader are the ones that you should look to for mentoring first. Even though you are just coming out of Basic, as an E4 you will be held to a higher standard than any new Private, so on top of seeking a mentor, it is also up to you to be the best Soldier that you can.
My advice is that you take initiative when you can, volunteer for any details that come up, and to also ask your Squad Leader to have the Schools NCO get you a spot at Airborne School. Well, okay, go to any school that you can, but make sure to get those Jump Wings.

I think you're looking for "how do I find a mentor" discussion? Correct? You'll "get what you get" within the organization you're assigned to. That said, embrace the three pillars of development (read ADP and ADRP 6-22) and get in-line with all three. One will require your unit and its organizational leaders to enable your development. Your operational experiences will likely shape how you become an effective leader -- every leader you encounter will touch your future leader DNA......either positively, or negatively. Take what you're exposed to, internalize it, and move forward with your own rationale thought and moral compass.

Take what you like as well as what you do not like from each leader you meet. From there, make them your own. It worked for me and I am sure it will work for you.

Find an NCO who is technically and tactically profecient within their career management field, is motivated to mission accomplishment, seeks greater responsibility, is not threatened by the concept of developing their subordinates, takes care of the soldiers under their charge,encourages self initiative and values educational opportunity. Attach yourself to this star, assist them and emulate their behaviors of exhibited leadership. You will benefit from their accomplishments and the mentoring relationship.

Throughout your career, you will find good and bad leaders, those you want to emulate and those you don't... but you can learn something from everyone. I had a great conversation the other day with one of my SPCs who is a marathon runner about why humans evolved the way they did and how we are built via evolution to be long distance runners (hint: we used to hunt by outdistancing our prey... fascinating subject). I would say at all stages, you look around and find people that you view as better than you are, and you emulate, then exceed what they do. This goes for the technical aspects of your job, your leadership skills, your physical fitness, and so on. A friend of mine in DEVGRU likes to ask the question 'am I better today than I was yesterday?'... that's a good mantra to live by.