Best Embedded SQL DB for write performance?
Check out the comparison on the H2 Site.
I'm using it for my Eclipse plugin and I'm very happy with it. Extremely fast for embedded use, very easy to use (one single JAR), great community support, highly recommended.
This benchmark from db4o might be helpful. It includes, JavaDB (Built on top of Derby), HSQLDB, SqlLite.
It seems HSQLDB out-performs its counterparts, especially when writing is concerned. H2, as a successor of HSQLDB, is faster than HSQLDB in both read and write with optimizing, clustering, transaction isolation features.