tubes: groove vs marshal

which brand out of these two would you reccomend for metal?
does the brand of the tube make in difference in the sound at all?

Since you've been so paient, yes their is a difference in brands, some brands sound cleaner, some dirty, some distort sooner or later than others, etc, it's really a personal preference that takes time and experience to develop, so I don't really want to suggest a brand, but Groove Tubes does offer tubes with different "Hardness" ratings, basically a rating of how the tube distorts, you might want to contact them and ask what they recommend. I don't know what model or year your Marshall is but you could even go with another type of tube depending on what you have, EL 34, 5881, 6L6, or 6550, can all and have all been used in Marshalls at one time or another, but depending on what you have, your amp may require some light modification to use a different type of tube, Hope that helps.............