Many thanks for your patience. If your employer offers you the choice between resignation and being sacked, there is no definitive right answer I’m afraid and it really depends on the allegations, the evidence, the strengths of both of your cases and also how far you are willing to take it afterwards.
I would say that if you are going to challenge them either way, a dismissal will be better to pursue as the burden of proof is on the employer, whereas with a resignation it would be up to you to prove that you have a valid claim.
I would however highlight the employer’s actions to them which suggest a decision may have already been made. Whilst pending a disciplinary you may have your IT access removed or restricted, they should not take other actions which suggest a decision has already been made (e.g. removing you from team structure, team pages, or something else which looks like a more permanent change is upcoming).
If you are offered a choice of how you leave it may also be worth raising the option of a settlement agreement where you are paid off to leave voluntarily and that could be a good way to part ways with a payment, without having to then make na claim against them.
Does this answer your query?