well If you are going to use large disks I’ve allays read ext3 over ext2, as ext3 is journaled and that will save some headaches with fsck and data corruption. as for drivers for windows, to my knowledge there are only ext2 drivers, but since ext3 is backwards compatible it’ll work just fine, and has for me for some years.
there are a lot of opinions about filesystems out there.
Just what I know: To read NTFS filesystems is supported in linux. I worked with it and it’s ok. But write support is still considered experimental by the kernel developers, so I wouldn’t rely on it at all.
Ext2/3 don’t have to be defragged, simply because they are good filesystems and hardly get fragmented (or only negligible). There may be other opinions, but don’t worry too much about it
About 6 months before I also worked with MS Windows and Linux. I created a “share” partition with fat32. It worked, but fat32 is painful (above all painfully slow) in my experience.
If you really plan to work for a long time with these dual boot configuration (and don’t switch completely to linux like I did), I’d try this ext3 driver for MS Windows.