What is the most agressive, tactical, attacking, line in this Mieses? [FEN ""]

1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Nf6 5.Nxc6 bxc6 6.e5 Qe7 7.Qe2 Nd5 8.c4 Nb6 


There are two variations here. Nd2 and b3. Which fits best to the criteria?
I think you are mixing some variations. In the main line Mieses, certainly 9.b3 and 9.Nd2 are two of the most played moves:

[FEN ""]
1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Nf6 5.Nxc6 bxc6 6.e5 Qe7 7.Qe2 Nd5 8.c4 Ba6 9.b3 {This is the main line.} (9.Nd2 {This is the third most common move.}) (9.g3 {This is the second most common move.})


However, in the position you are concerned with, you may be much more aggressive than any of those moves. Black has wasted yet another tempo with his knight, and bear in mind that you don't need to overprotect the c4 pawn as it is already protected by two pieces. Possibly the best move is to develop another piece and go for a mating attack as early as possible:

[FEN ""]
1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Nf6 5.Nxc6 bxc6 6.e5 Qe7 7.Qe2 Nd5 8.c4 Nb6 9.Nc3! {The knight can be developed to a more active square, and has more control over the center, which will be extremely important, since in the main line black gets a passed pawn and white will need to control it.} Qe6 10. Qe4 g6 (10... Ba6 {Should also be looked at for white.}) 11. Bd3 (11. f4 {Is a possible different move order, perhaps over aggressive, which may transpose or get into completely different territory.}) Bg7 12. f4 O-O 13. O-O {This is more or less a common subvariation of the Mieses.} Ba6 14. b3 d5 15. cxd5 cxd5 {Around this move, the book/theory begins to get fuzzy and some other interesting responses have been tried.} 16. Qe2 (16. Qf3 {Is also to be considered.}) Bxd3 17. Qxd3 c5 18. Ba3 Rac8 (18... Rfc8 {Is also valid, but offers slightly smaller chances.}) {This is the main subvariation line, but quite a few digressions are possible.}


Although the position is roughly equal, maybe with a slight plus for white, to make a small mistake is very easy, and those mistakes come with great doses of punishment and pain, since a little slip in these lines will very likely cost the game. White has to be constantly looking out for moves like f5 (which can be played even if the bishop has not been fianchettoed) and black has to avoid getting crushed by the bind the e5 pawn makes. This is not a position you can play mechanically and positional, but a very complex tactical struggle.