You speak about "Counter offer by current employer," but I would like to know what you feel about this offer. Is this a better offer than the new employer has offered you? And do you feel you can get more good opportunities and growth with the new employer than the present one, or what are you expecting from the new employer in comparison to your present employer?
See, you have spent a good time here, I presume, and are well familiar with the work conditions and everything with your present employer. Therefore, you are the one who can judge these conditions first and have to decide which is better for you. Please let us know what you feel about it too.
Second, do not forget to consider the reasons that put you in this condition. Reasons which forced you to resign from the present position/employer. It is also important to realize that this "Counter Offer" evidently shows how important you are to your present employer, and they appreciate your skills and work performance, which is why they want to retain you.
Apart from that, in simple words, I would suggest you accept this counteroffer and continue with your present employer. For this, why you should continue with your present employer, I would also like to present some other facts that will help you understand the same for sure.
- You are well familiar with the present work conditions and others with your present employer, which enables you to work with a good understanding. But with a new employer, to get the same, you are certainly going to take time (if you join), which is why you should continue with your present employer.
- You have resigned, but still, your employer likes to retain you. That speaks about your work performance and the trust they have in you, which I believe is important for an employee and gives you more chances to strengthen your position there and further promotions.
- A counteroffer automatically means a good hike in salary and other benefits, more growth options, work responsibilities, more learning, and a value that an employee holds for an employer. The same is not easily or early expected from a new employer. Every employee wants to be an essential part of an organization, expecting value with respect and a strong, good position that matters too, and with your present employer, you are getting the same.
- You can get many new and better offers in the future with many reputed employers/firms, but the value and trust you have gained are not so easy to earn. This is why I feel you must continue with your present employer. Also, in this outer world, opportunities always follow the right, skilled, and experienced candidates, so you can get the same in the future whenever you feel like moving on.
Now, I would like to refer to the statement/suggestion provided by Ms. (Cite Contribution) that you must be honest with yourself and your new employer. Please tell them that you are not going to join them (if you decide to continue with your present employer), which will also be a good example of professionalism.
Lastly, I would suggest you consider the reasons for your resignation before making any decision, and I'm sure the same will give you a lot more to learn for your future and career.