Here’s another good opening choice for juniors and other improvers, the 3.Bb5 Sicilian. There are lots of things I like about this opening with the main one being how it illustrates sound opening principles. White develops quickly, castles early and plays for the centre.
Many of the openings I’ve seen recommended at junior level fail to illustrate principles as well as this. For example the ever popular Fried Liver Attack (1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5 Nxd5 6.Nxf7 Kxf7 7.Qf3+) moves a piece twice in the opening and then gets the queen out. Teaching principles alongside such lines can be confusing to say the least.