I mainly like to be different I guess, but I decided to level and alt as Prot from the very beginning, and I decided to put all of my points in the Prot tree at the start. The main reason for this is I like to do instances in appropriate level groups, and I don't like to do the Deadmines until I hit level 20 or 21 and have my level 20 Paladin Quest (no sense in doing Deadmines more than once in my opinion, even if the second time is just a partial run for the wood).
At level 20-21 if you have improved RF already, tanking Deadmines is cake, doing part of SFK for the Paladin quest is easy, and a few levels (at most) later Stockades is cake too.
If you aren't an alliance player, this would probably still apply but I am not aware of all of the details of the level 20 Paladin quest for Horde.
Also, if you have higher-level characters run you through the dungeons you need, this is also not necessary. I personally hate having a high-level "run" me through something. I like to group with appropriately levelled people and help them to learn some group mechanics even early on.
It is of course perfectly possible (and not even difficult) to tank the early instances as Ret Spec and I have done so in the past. I think it is just the ********* in me that makes me want to spec this particular alt as Prot from the very beginning. I have Questhelper and Cartographer though, and I certainly don't seem to be having any problems killing everything at a reasonable pace.
Edited, Nov 26th 2008 12:00pm by jeromesimina