There are several threads on this forum about this very issue. I prefer reiserfs as it is faster and more efficient than ext3. XFS can be used with 32 bit systems without any problems that I'm aware of (as I have used it several times with VL on my 32bit system). It is not recommended to use it on your root partition if you want your boot-loader in the superblock of that partition. XFS is touted to be at its best when manipulating large files (e.g. 1Gb or larger in size). Perhaps a few things in ext3's favor is that it has been around for longer than the other two and if ext4 ever gets out of development there would probably be a way to convert ext3 to ext4. Time will tell on that one. There are several other nuances that are interesting to consider but unless you are limited in resources (processor, disk, RAM, etc.) all will probably perform well with little if any perceivable differences.