When comparing Swift with eSoft Planner - the main differences are in usability (both for you and your customers) and active development.
eSoft Planner is notoriously difficult to add & edit bookings. For you and your staff, adding recurring bookings on the calendar is a very tedious process. The online booking portal is also hard to navigate - which means you likely won't see a drop in call volume from athletes and parents. In comparison, Swift has an industry-leading mobile-first booking flow - guaranteed to be better for your athletes and your front desk.
eSoft Planner (as far as we know) is also not being actively developed. There's been no major changes in the tool for the last 8 years. This means that if you have certain requests or features you'd like, they will most likely not be built. Meanwhile, Swift is improving almost every day - the team is constantly looking for feedback and shipping new improvements to make your lives easier.