Your question cannot be answered here. The credibility of any witness - felon or not - is unique to that witness and cannot be generalized. A great deal depends upon the evidence/information presented about the witness, the witness' demeanor, the nature of the case, the nature of the evidence the witness purports to present, etc. This is definitely something that should be discussed in private with your attorney.
The law only says that, subject to some highly technical rules, the felony conviction can be brought to the attention of the trier of fact, i.e., the jury or, in a bench trial, the judge. It does not say how much weight the trier of fact should give this information. That is a judgment call that depends on the details of each case and also on the individual opinion of each juror or trial judge.
Credibility is decided by the trier of facts in the court of law.
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The trier of fact ultimately decides on the credibility of a witness
The response above is not intended as legal advice. This response is for educational purposes only. I have not met with you and I am not knowledgeable about the specific details of your case. Each case is unique and different. Therefore, it is highly recommended that you contact and meet with a licensed criminal defense attorney to discuss your specific circumstances. In addition, an attorney-client relationship is not created by virtue of this response.
Under the federal rules of evidence most felonies can be used to attack the credibility of a witness and in some cases even misdemeanors that involve dishonesty can be utilized for the same purpose. If the conviction occurred more than 10 years from the date the conviction is sought to be used it is often excluded with some exceptions. Ultimately, as many of the attorneys responding to this question have said, if the conviction is used at a jury or bench trial, the weight to be given to it is left to the fact-finder--the jury or the trial judge.
Beauty like credibility is in the eye of the Beholder. The Beholder in criminal cases is a complex combination of the rules of evidence and the judge's interpretation of the applicable rules. Assuming that the admissibility of the testimony has been dealt with and allowed then the question becomes how much weight (value) does the testimony of the felon have in the particular case. Here again weight is determined by the trier of fact, in a bench trial that means the judge; in a jury trial that means the members of the jury during deliberations. Prior to deliberations the jury is not supposed to decide or discuss the issue of weight.
Of course, every answer or response is based on the information provided in the question asked and requires a much more complete context than is available in this public forum. This answer/response should NOT be relied upon to make any legal decisions. Seek the advice of an experienced Federal and/or state criminal defense attorney in your jurisdiction BEFORE you say or do anything.