ext2 is quite old, ext3 was the standard for a very long time, but in the last couple of years ext4 has surpassed ext3 as the default in most distributions. There's no reason you shouldn't go with ext4 IMO, all of the major bugs have been worked out and it's quite stable and reliable.
This should give you some more insight into the advantages of ext4 over its predecessors:
One of the big advantages is in timestamping. ext3 only provides second granularity in timestamping, ext4 provides nanosecond. While this might not concern you too much, one of the bigger issues is the year 2038 problem
with ext3, which is becoming more and more important as that date gets closer. Yes it's still 15 years off, but we are easily at the point now where a computer constructed today could still be operational when this rollover takes place. It's very important to start planning and preparing for it IMO, which means ext3, and many other filesystems, are out of the running for any machines set up from now on.