personal playstyle. Let's take a look at the advantages of each. Sometimes you will simply be first or second based on a dice roll or predetermined role in a battleplan, but other times you will have the option to choose whether you go first or second, and the choice you make could well shape your success in the coming turns. Be sure to check out our other tactics articles for more advice.
Some armies depend pretty heavily on lots of command abilities or magical buffs. If you want the items from your hero phase in effect you need to have taken your turn before they take place. Mystic shield and inspiring presence are great ways to reduce the damage your force will take in the following turn, but if you haven't had a hero phase to trigger them in, they aren't in effect and will do nothing to protect you. Going first allows you to place some defensive counter maneuvers onto your units before your opponent can strike at them while they are exposed.
Going second can also let you see what your opponent plans to do to some extent. Perhaps they deployed in a way that gave them multiple options, or it wasn't clear what their intentions might be. Like going second in Chess, taking the second turn in AoS forces your opponent's hand and gives you the potential to see openings and vulnerabilities in your opponents' movement plan before you expose any of yours.
Depending on many factors like table size, movement value, interceding terrain, etc, going second may give you a better chance of getting the charge instead of being charged. Certain units benefit from being the charging party in a given combat, and it always allows you to select which unit strikes first, so if your opponent does the first half of closing the distance for you, then going second may allow you to be the one successfully charging your opponent and having an advantage in that phase. On larger tables or with units that have smaller weapon ranges or movement values, it may also allow you to shoot at your enemy after your move, while they would not have been in range before your movement brought you two closer together, giving you a round of shooting over your opponent's forces as well.
As discussed in the "Going First" section, spells and command/hero abilities happen BEFORE movement, so you may not be in range for a spell, debuff, or attack on an enemy unit unless they have already moved closer to you. This of course carries the risk of being hit before you can apply defensive buffs, but if that's a risk you are willing to take, going second will suit you well. If you have a magic-heavy army, your targets will usually be out of range of your arcane bolts and what-have-you before a movement phase or two has happened, and first turn may preclude you from landing with any meaningful magic offense.
How have you experienced turn order in AoS? Do you prefer first or second turn to start the game?