There are many differences, but some of the things I like the most about Swift are:

• Safer type system, (e.g. no nil outside of Optionals)
• Mutability is discouraged, (but still possible if required)
• Type inference
• No headers
• Better support for concurrency
• Easier to learn & easier to maintain
• Much better support for the functional programming paradigm
• More powerful enum types
• Reference compiler is open-source and development is done in the open
• Playgrounds, (code is executed as you type is)
• Linux support