If we consider the traditional Java approach the answer can be deducted from the quote bellow as being much slower:
Because reflection involves types that are dynamically resolved,
certain Java virtual machine optimizations can not be performed.
Consequently, reflective operations have slower performance than their
non-reflective counterparts, and should be avoided in sections of code
which are called frequently in performance-sensitive applications.
Quoted from the JavaDoc about reflection – http://java.sun.com/docs/books/tutorial/reflect/index.html
So since Spring uses Reflection with the getBean() method the SpringContext.getBean(SomeClass.class); approach should be slower.
EDIT:
Also note that the ThreadLocal also has caching embedded so as long as you reuse information in those threads it’s for sure faster.