First Let See Torterra Stats
Torterra Stats :
HP : 95
Attack : 109
Defense : 105
Sp Attack : 75
Sp Defense : 85
Speed : 56
secondly You definitely know :
1. Solar Beam have 120 base power and Energy Ball have 90 base power, Solar Been have 25% power higher than Energy Ball
2. However Solar Been don't have additional effect and Energy Ball have 10% change to lowering target special defense
3. Solar Been is charge move, however since you have power herb is not problem
Both is not bad move, however Torterra Attack is higher than he special attack, I suggest you can go with earthquake or seed bomb, both have power bigger than Solar Been and Energy Ball, by the way if you want special attack move, you can go with Solar Beam if you want use I competitive battle since power herb is single use in game, and go with Energy Ball if you want play in game only, hope help