Your question, "What is the best Wordpress theme for my blog" is nearly impossible to answer. There are an incredible number of factors that go into website design to influence conversion, sales, and user experience.
A theme out of the box probably isn't the "right" answer for long-term success, but it may get you up and running. I don't think website design is ever "done". Think of megasites like Amazon or Facebook, they are constantly changing an testing.
That said, to set yourself up for growth, the ability to A/B test, change details and layouts, etc, I recommend a custom theme builder similar to Divi by Elegant Themes (www.shaunnestor.com/recommends/elegantthemes)
They have a number of pre-built layouts that you can use as a foundation, but changes as your needs fluctuate.
All the best,
As far as where to look, I'd start with this list of frameworks, and email them directly to see if they recommend a specific theme for your service niche:
There are many factors to consider when purchasing a premium theme:
1.) Is there an active support community? This should be at the forefront of your mind, as there's nothing worse than needing support only to find out that it's an outdated theme that doesn't get regular updates. Take a look at the changelog and see how often updates are pushed. Ask them about support turnaround time.
2.) Speed of theme - You don't want a theme that is bloated and will slow down your site.
3.) Aesthetics - Spend some time taking a look at demos of their theme. See if there's some sort of 'showcase' that shows other sites using that theme. Peruse those sites
4.) UX/UI - Is the theme intuitive enough to navigate around? Can you add your own custom CSS if necessary? Maybe you're not tech savvy, but if you decide to have customization done, you can always outsource having CSS written for you, which you can then add in the appropriate section within the theme's settings.
5.) Framework - Is the theme that you're considering part of a larger framework? For example, Themeforest is a framework that provides many different themes.
6.) Reviews - Check the reviews/testimonials on the theme.
Let me know if you have any questions :)
As a WordPress user myself, I find it helpful to test out different templates and see which one resonates with you the best. WordPress has lots of templates to choose from, my current theme is Pique which I feel you should check out. Also remember that you can add your own personal touches to the theme to make it more appealing!