Squarespace offers a ton of templates to choose from. But for the most part, they all do roughly the same thing except for just a handful.
Since designing over 400 websites with Squarespace for all kinds of businesses, I've used just about every Squarespace template they offer.
Best Squarespace template for Blogging
My favorite template for blogging is the Five template. Five has a very classic, simple blogging layout, with the ability to have a side column on the left or right. Most other Squarespace templates do not offer a side column at all, so Five is really the only option if you want a traditional blog layout with a right-hand column.
View the Five template here: https://five-demo.squarespace.com/
Best Squarespace template for Portfolios
My favorite non-ecommerce template is Pacific. It's one of their older templates, but it works great for full-width images, and yet is still flexible for other styles like full-width galleries, or simple text pages. It's versatile yet simple.
View the Pacific template here: https://pacific-demo.squarespace.com
Best Squarespace templates for Ecommerce
For all other businesses, I recommend that you look at their Online Store templates. These tend to be the most up-to-date templates with the most features. The newer Squarespace templates have a Shopping Cart icon integration with customer Accounts, and search bars at the top right. They also allow for Quick Views for ecommerce product searching, and have a ton of design customization that can be easily customized with their Style Editor. In terms of choosing the design, I recommend you pick the layout that you like best, as they all roughly have the same features and can be more easily customized than any other template, so you shouldn't have to worry about picking the "right" one, since elements can easily be moved around with their Style Editor tool.
View all the Online Store ecommerce templates here: https://www.squarespace.com/templates/online-stores