In this case, it's very difficult to answer this question. A casual player, usually has little time to play during a week, but there still is a way to rise your leveling efficiency to the maximum and level as fast as possible. As I said before, questing is the best way to gain XP for a WoW character, but just doing random quests will only lengthen the time you're spending with your XP. A WoW leveling guide, like the one I use, arranges all the quests in the best order so your time wastage is reduced to nearly zero. I can tell you that a good WoW leveling guide has an optimized quest path, therefore you'll be able to know what are the best quests for your level, where to go and exactly how to do them so that your leveling session will bring your character the maximum of XP. With a tool like that you won't even need any other addons, a guide is the ultimate addon itself and works as an in-game GPS device that will show you the way.
If you want to get all the professions and do all the dungeons and instances in WOW then you might not need a Horde Leveling Guide to help you as it does not matter how much time it takes you to get to level 70 and the instances and dungeons with a good group or guild will soar you through the levels anyway!
However if you want to get to level 70 as fast as possible and are not really that bothered about the instances and the extras then a good Horde Leveling Guide can really help you.
What is contained in a Horde Leveling Guide?
Well normally a horde leveling guide has been written by a speed leveler for World of Warcraft and this basically means someone who starts a brand new server on the game and times themselves running through the levels to get the fastest playtime. As you can imagine it would take many weeks or years of playing to find the fastest route through the game so this is quite an achievement!
Then they write a guide showing you the path that they took and they normally contain maps and text that tell you what to do to level faster.
So they can be very helpful and if you are getting a bit sick of the game and do not really think that you have enough time to invest then it is worth looking at.