Deciding between targeting small businesses or enterprise

Go with where you have more direct customer access, because winning the first customers will be the hardest.

If you don't have at least 1 entreprise customer that you can sign up from your network on day 1, then I would go for SME. Sales cycles for entreprises can be +12 months, even if they are really interested in your solution. This means you'll need 12 months to find out whether anyone really cares for your product (which is terrible). The only caveat is if you have a great network and can bring 2-3 large customers from day 1.

I am more of a B2C guy, but this is a difficulty I've seen with many B2B companies that underestimate sales cycle significantly.

I've recently spoken to the CEO of a successful startup that has been growing its workforce like crazy. I asked him why not just stay 10 people and swim in profits (their SaaS service allows it) and he explained that a big enterprise client expects a team of around 10 workers dedicated to its needs.

Unless you have a really good way to get your first enterprise customer, I'd go SME.