I was going to comment on this post over at From the Fang. However, I found that I had the same problem as them in that I had too much to say so I thought I'd post something here instead. Now, all of this is based on an article over at Space Wolves Blog which led to some discussions about whether Wolf Scouts were better than Land Speeders.
Now, personally I like both of these units. To start with, let's have a look at what I'm running in my army;
Wolf Guard, Combi-Melta, Power Fist
5 Wolf Scouts, Meltagun, Mark of the Wulfen
Land Speeder, Multi-Melta, Heavy Flamer
Land Speeder, Multi-Melta, Heavy Flamer
Just for comparison, the Scouts cost 143 points and the two Speeders are 140.
From this point of view, both are incredibly flexible. The Scouts can set up normally (although I've never seen anyone do this), Infiltrate or go Behind Enemy Lines. The Land Speeders can set up normally, go into Reserve to speed on from your board edge or can Deep Strike. Now obviously, going into Reserve, there's always a chance that your Speeders or Scouts won't come on until Turn 5. Also with BEL, there's a chance that you'll enter via the wrong board edge. However, the fact that they can come on the right edge can make your opponent think twice about their own deployment.
The Speeders win this hands down with their 24" move. You can pull the classic Eldar last turn Objective contest and of course you get your 4+ save. Of course, there's a caveat here - if you've infiltrated or gone BEL with the Scouts then there's a decent chance that you don't need to move 24" to get to where you need to be.
Now, I'm sure we've all had "Melta" syndrome; where you always miss with a single Melta shot. This is the problem I always seem to have with my Land Speeders. They Deep Strike in, miss with their Multi-Melta and are then left swinging in the wind. I had exactly the same problem with the Scouts which is why I added the Combi-Melta into the unit. However, they have the same problem against AV14 which is if they miss, they're in trouble.
Obviously the Scouts win this one as they can actually launch assaults. However, with their speed, it should be relatively straightforward to keep out of the way of assaults (I say should, as I always get too greedy with regard to firing both weapons and so mine get dragged down quite often)
It's very easy to get 4++ saves for both units. The Scouts are at home in cover and the Speeder can Turbo Boost as mentioned above. However, the Speeder has the same problem that all vehicles have in that a single shot can take it out. It also has the problem that a single Boltgun can shoot it down.
Now one of the things that Land Speeders are great at is blocking; they can be awesome at slowing down the enemy. Similarly, the Scouts can be a great speedbump if they Infiltrate.
Ease of Use
Personally, it took me a long time to work out how to use Land Speeders effectively and I'm still not an expert. Conversely with the Scouts, I found them easy to use from the first game. I sent them BEL and used them to attack enemy heavy weapons teams or vehicles in the enemy's backfield.
So, which is better? I think they're both excellent units and they are tools that every Space Wolf player should use. However, if I had been picking one for Adam's Top 5, I would have gone with the Scouts. There are two reasons to this. Firstly, they are a unique unit in the Space Wolves codex. As much as I love Speeders, they are generic Marine units and available to every man and his dog (even the Tau and and Eldar have their own versions) Secondly, whenever I've dropped my Scouts from my list, I have really missed them whereas I've always felt like I could cope without the Speeders.
Well, that's my opinion anyway. I've not really talked about army builds but that is always going to affect which unit works better for you. I think people will always prefer one unit over the other and they will always have evidence to back up their point of view. As I said, I think both units are effective so rather than getting loads of comments along the lines of, "This unit is best, I always use it and it's always fantastic", let's here about which unit you prefer, what kind of army your use it in and how you use that unit to its maximum efficiency.