What RUU do I need for my HTC phone?
Both.  Bravo is HTC's internal codename name for the Desire.  They do this as they want a constant name for internal purposes as they often sell the identical device in multiple markets under different names (e.g. the HTC Magic is also sold as the HT-03A, the myTouch 3G, and has the codename Sapphire) or multiple devices (e.g. GSM and CDMA versions) under the same name (e.g. both the Marvel (GSM) and the MarvelC (CDMA) are both sold as the Wildfire S).  HTC does it with names, Samsung uses model numbers, same basic idea.
No, not unless you want to stay at your current version for some reason.  RUU means ROM Update Utility.  For most purposes, you most likely want to go with the newest not-carrier-specific RUU to have the latest update so you have the latest Android version and radio firmware.  The RUU is the master update-everything.  Android, radio firmware, and h-boot.  It does it all.
WWE is World Wide English.  It includes all languages they translate for.  The English bit indicates that English is the base language and all other languages included are translated from English, rather than being written directly in those languages.  The ARA bit indicates the same thing, but that the base language is Arabic.