There is absolutely no difference between both.
If you take a look at the standard :
7.1.3 The typedef specifier [dcl.typedef ]
A typedef-name can also be introduced by an alias-declaration. The identifier following the using keyword becomes a typedef-name. It has the same semantics as if it were introduced by the typedef specifier. In particular, it does not define a new type and it shall not appear in the type-id.
7.3.3 The using declaration [namespace.udecl]
If a using-declaration uses the keyword typename and specifies a dependent name (14.6.2), the name introduced by the using-declaration is treated as a typedef-name.
However from this page : http://en.cppreference.com/w/cpp/language/type_alias
It is said :
Type aliases are similar to typedefs, however, have the advantage of working with templates.
It seems that this
// template type alias
template<class T> using ptr = T*;
// the name 'ptr<T>' is now an alias for pointer to T
ptr<int> x;
is only possible with the using directive.
And do not forget that this is a C++11 feature. Some compilers do not support it yet.
