"A" seems fine to me. I do not see a problem with it. Why do you think it implies that it is no longer among your first experiences?
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AnonymousWhich of A or B is better?A is better. Obviously your first experience was in the past.
AnonymousIf I use with, do you guys think it would imply I worked with the facility ... in a way(s) where I was not physically there?It could certainly mean that. I'd keep "at".
Anonymousthe condescending tone of your response was hurtful.I apologize because you found it hurtful, but I had no intention of being condescending.