The past version of Doomguide was available just to clerics but now also paladins can choose to become one so this is my first dilemma: according to Doomguide "standard" background (I know that in my personal FR anything can happen, but i always prefere to follow the original FR), who is more suitable to become one? Clerics or paladins? Or maybe even invokers or avengers? According to the -short- description, i personally think that paladins would best fit the role of undead-hunter.
Do you guys like this class? Suggestions are welcome!
I think Paladins make for better Doomguides in 4th Edition because Paladins fill the defender roll and are exceedingly capable of drawing enemies in close and making them focus their attacks on the Paladin. This fits the flavor perspective in the sense that intelligent undead will know what a Doomguide's purpose it (i.e., destroy undead once and for all) and will work hard to eliminate a Doomguide if one is ever encountered.
I think Paladins make good Doomguides because the role of questing holy warrior fits the Paladin concept.
If I were a Dungeon Master with one or more Doomguides in my group of players, I'd pit them against the Eminence of Araunt as fast as possible. The discovery of snippets of the Codex of Araunt and the idea that there are undead "kingdoms" stretching all over Returned Abeir and Faerûn ought to be enough to start a Holy War, in my opinion. 
I don't know all that much about Doomguide lore (have they ever been featured in any novel fiction, I wonder?) but hopefully someone more knowledgeable than I will come along to confirm this.