Land Speeders are often hailed as being too good - at least from the Marine opponent's perspective. Tournament lists are often littered with Tornados, which is understandable since it's in essence a very good vehicle.
Land Speeders are fragile by nature though. Despite Skimmers Moving Fast, it has a low armour value and it is thereby easy to get a glancing hit on them, which will either result in it hiding for a turn and not shooting or it being killed.
They are arguably the fastest vehicle in Codex: Space Marines though, capable of moving as far as Bikes, but they ignore terrain due to the skimmer type. This makes them excellent objective grabbers if you go second and also good harassing units against especially enemy armour.
In this article, I'm going to go through all the kinds of Land Speeders, not just the ones you see in tournament lists. There are several different patterns, and almost all of them are at least usable.
Heavy Bolter Land Speeder:
The vanilla type, with no additional weapons, no upgrades and so on. This Land Speeder has two advantages: it has a pretty good armament with good range and it is cheap. The armament's range allows it to stay out of range from some of the smaller-calibre guns that are often lethal to Land Speeders when massed.
Despite the cheap point cost, the Heavy Bolter Land Speeder is rarely used. This is due to the fact that the Tornado is simply so much better - even though it's not as cheap - and because the lone armament on the Land Speeder makes it easy to destroy it or rend it as nearly useless.
If it lose the Heavy Bolter though, just hide it until turn six and then grab an objective.
Multi-Melta Land Speeder:
The Multi-Melta Land Speeder sees play sometimes, and it can definitely be an effective vehicle, since it can destroy a tank worth more than 2 times it's price in points on turn two, with a single shot. It is more expensive than the Heavy Bolter Speeder, and has a shorter effective range, but in turn it is much more powerful, being able to wreck havoc upon a unit
The general idea is to deploy these on the flanks, advance a full 24" the first turn and hide behind terrain. Move it out on the second turn against the closest tank, and pray you don't roll a one or a two to hit.
As they are by heart a sacrificial unit, they don't make for good objective grabbers - they are sometimes more likely to be gone by turn 3 than even Tornados. If it suffers an armament destroyed result though, the best idea is usually to just hide it and swoop it in on turn six, just like the Heavy Bolter Land Speeder.
Tornado with Multi-Melta and Heavy Flamer:
Tornados comes in two different weapon combinations: Heavy Bolter and Assault Cannon or Multi-Melta and Heavy Flamer. The Multi-Melta and Heavy Flamer is most often a useless, and is definitely the worst Land Speeder of the lot. This is because it is expensive and it has mismatched weapons. Multi-Melta is great when mounted on vehicles and Attack Bikes, since it makes for a good and mobile tank hunter. The thing is that the regular Multi-Melta Land Speeder already fills this role, and it is considerably cheaper.
Heavy Flamers are great for frying infantry, but taking on infantry is something that the Assault Cannon and Heavy Bolter Tornado does much better, and again, it is cheaper than this Land Speeder.
Because there really is no units in the game that you want both weapons at the same time against, the Multi-Melta and Heavy Flamer Tornado is generally labelled as "overpriced", "useless" and "sad". I would only take it for strict fluff purposes.
Tornado with Multi-Melta and Heavy Flamer a.k.a. "The real Tornado":
This pattern is why Land Speeders generally are labelled as overpowered and even cheesy. This Land Speeder sports an Assault Cannon, which is the best weapon in the game hands down, and thus, people hate it.
Still, this is the Land Speeder if you're going to take them. "You can't really go wrong with a pair of Tornados" is a common quote around Space Marine forums, and they are in essence correct. Two or three Tornados will provide a firebase with both awesome shooting power and great mobility. They can take on almost anything in the game, they are relatively cheap and they are also good in almost any kind of Space Marine armies. Static shooty armies often brings them as the mobile splash in the list, fast assaulting armies often brings them for support and so on.
Tornados are pretty easy to use. Just move them up behind cover until they are in range, and unload with both weapons. That's all there is to it, which I am sure adds to the cheese label. They suffer from a severe weakness though: The Assault Cannon, despite it being the best weapon in the game, has a limited range which requires the Tornado to get within Bolter-range, effectively cutting its lifespan drastically.
Land Speeder Typhoon:
The final pattern is the Typhoon. It is armed with both a Heavy Bolter and a Missile Launcher. This makes it stand out in the tactics department compared to the Multi-Melta Land Speeder and the Tornado. When a Land Speeder of a different weapon outfit has to get close to employ its guns at full effect, a Typhoon can stay safely out of range from small arms and fire both its weapons.
It is cheaper than the Tornado, and it is a wise decision for those who wants something else than the common Tornado. It's not quite as good, but still viable in the right army.
But what about the squadrons?
The entry says Land Speeder Squadron, not just Land Speeder. You can have up to three of them in a single Fast Attack choice and you can also mix Land Speeders of different patterns within a squadron. This makes for some really cool units, but the effectiveness is lowered by the rules regarding shooting at vehicle squadrons. As stated on page 73 of the Warhammer 40 000 rulebook, you have to spread out the hits evenly, which means it's possible for a unit of enemy infantry to rapid fire an entire squad of Land Speeders and damage them all.
So the general rule is to take only one Land Speeder per Fast Attack slot. There are always exceptions, if you are trying to cheese up on Land Speeders, just try and spread them out and make the squadrons as small as possible. Two Land Speeder Tornados working together is good, or at least viable. The best part is that if one of the Tornados goes down, the unit is still scoring.
Land Speeders are fast, offensive and fragile. They do make for great objective grabbers - either to net you Victory Points, or rob some from your opponent, a couple of them can really hand it to the opponent in the shooting phase but they all fear the retribution. Stay away from Bolters and the Multi-Melta/Heavy Flamer Tornado and you'll do fine with any Land Speeders you bring.