JTDS is open source (LGPL), the other is proprietary, created by sybase. In terms of what is best, you have to navigate.
Sybase calls its latest JDBC jconn4.jar, so the version you are referencing only matches the JDBC 2.0 specification. JTDS complies with JDBC 3.0. Whether it matters or not, it depends on the version of Java you use to run your application.
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