After removing from a vacuum pack you'd want the tea to acclimate for a while. I generally find that if I dump it into a tin, then about the third time making some is the best -- i.e., after opening the tin a few times with a day or so in between.
If there's any discernible roast, then the tea will go through changes for the first year, and will be better after it has settled.
Also, no vacuum sealer creates 100% vacuum, but some are better than others. If I remember right, the typical home sealer gets about 70% vacuum, and more commercial ones get somewhere between 80%-90%. (That's why some put oxygen absorbers in the package.) So how long a tea stays fresh in a vacuum pack will depend partially on how complete the vacuum is.
Regarding bags vs tins, I don't trust bags because I don't always seal them completely, and I've also had the zip seal separate from the bag and I didn't realize it until it had been like that for some weeks (or longer). However, you can reduce the amount of air in a bag before sealing it, which you obviously can't do with a tin.