When defending a suit contract it is generally best to find a “safe” opening lead if possible. Safe leads are ones where you are unlikely to give up a trick. This is the only time you have to play a card without seeing dummy.  Safe leads include top of touching honors,  partner's bid suit, xxx xxxx. Less safe leads are low from unsupported honor, leading an unsupported honor, or from a low doubleton. The two agressive leads to consider are a singleton when you have it, or an unsupported Ace from length when partner is likely short. 
On this auction dummy is more likely to hold side suit honors than declarer. So that makes leading an aggressive minor suit A a little less risky.  But I would still choose a spade, whatever you lead from 3 small. 
 

While your hand meets the criteria for a week 2♦ bid non vulnerable, 6-10 hcp 6♦ , the 5 card ♠ suit makes it a no. It’s advisable to avoid preemptive bids on hand where you have 4+ in a side major. When you preempt, there is an implication that you are one suited. Therefore partner will not bother to seek a fit in another suit unless they have a very good hand with a good 5+ card suit of their own. The risk of missing a spade fit outweighs the benefits of preemption.