Depends what you are looking for.
TradeStation used to be pretty good, but it's outdated (by at least 10 years), and runs only on Windows. Also, their commissions and platform charges are pretty high, not a very good choice unless you account is at least $100K+, and preferably 250K+ The positive side is that it's more user-friendly for non-technical people, and their programming language is though very primitive is easy to understand and implement simple strategies with, especially if you have little programming experience.
I've switched from TradeStation to Interactive Brokers a few years ago - they offer lower commissions, no platform fees, great APIs, and you are not stuck with a proprietary and an very limited EasyLanguage, instead you can use much more powerful Java, C/C++, even Excel/VBA. Plus it runs on MacOS, Linux, and Windows.