Ok well raiding cavalry and throwing axemen take too long to make in an early stage where you need guys fast as norse. They are made at the same speed as greek units but are less powerful. This means that a greek player can have the same amount of units but have each individual units be much better. For instance in the same basic timeframe a greek player could have 10 hippikons and the norse player would only have 10 rc. Rc is inferior 1v1 with hipps so you will lose.

This is why i think that ulfsarks are the best norse unit. They build in 9 seconds. Greeks cant outmass them early on and eggy can only have the same amount of units but their units are inferior to norse ones. Basically in the same amount of time you could build 2 ulfs and 1 rc. There is nothing that 1 rc can do better than 2 ulfs. Of course 2 ulfs take up more pop and cost more. However early on in the game when a norse player should secure the win pop wont make much of a difference since you wont have hit pop limit yet. Cost wont make too much of a difference either because there are many builds that allow for constant ulf production out of 3 longhouses. Now that we've established that lets go over the pros and cons of the unit and see if that is why they arent used much

Pros
Built fast
High attack
Good speed for an infantry unit
Good LOS means you can find their villies better]
With massed ulfs you can build buildings fast

Cons
Low hp
Low pierce armor
Infantry have a lot of hard counters

This seems to show that they are a decent unit. They have a good cost in that they dont cost an exorbitant amount of any resource. Ok i will show how to avoid having their weaknesses come out

Low hp: Basically try to get healing as soon as possible (odin regen, valks, or healing spring)
Low pierce armor: Basically against towers just take them down as early as possible because unless they are eggy you can get them down before they actually become towers. Against eggy stay out of their way if they have houses around them otherwise kill them. However another tactic is to take down one house and tell a few of your ulfs to take down the tower. Chances are they wont have boiling oil so you will do fine. Against ranged units like toxotes just upgrade your pierce armor and take out the buildings they are made from before enough of them can be made. This is easily done since they are made so fast and norse can advance quickly
A lot of hard counters: Much like ranged units try to take the buildings out before they get in mass. However its also a good idea to just attack them while you outnumber them since 10 ulfs will still beat 4 axemen. If they start massing hard counters just make rc and spam towers. Bye bye hard counters.

Basically ulfsarks can be massed early and allow you to overwhelm him before he can react. This is what norse is all about and fits perfectly into their style. Every norse civ is good for ulfs here are their strats.

Loki: Build a FB as usual and as usual get some hersir. Then use your 10% faster longhouses to pump out ulfsarks even faster than usual. Basically a loki rush with ulfs. The loki rush is about getting a large amount of units destroying their base early so ulfs are the best for it. Later on in the game go bragi to get uber ulfs.

Odin: Get lone wanderer to have uber raiding ulfs. Lone wanderer ulfs dont get hit much by towers and are fast enough to get away from any of their counters. Just surprise him by raiding him with 8 ulfsarks by 5:30. Then jsut keep the raiding up and speed build towers at all the gold. They are better raiders than rc for a few reasons. One is that they dont get hurt by crenellations. The other is that they have a huge LOS allowing them to actually find enemy gathering sites very quickly. Just act like you are massing rc for raiding except make ulfs instead. They are built fast and you can raid them well. Also use you ulfs buidling killign skills to take down military buidlings.

Thor: Get to classical at 4:30 using a lot of dwarves to get there that early. Pump ulfs out and just ravage buildings, do the occasional raid and tower gold. Get an armory and upgrade pierce armor a lot if against greek and attie, hack armor a lot if against norse, and upgrade hack armor a lot when against eggy but also get a pierce armor upgrade or two to combat the tower fire. This should make you hard to kill except by hard counters. Make sure that you engage any army they may have to stop them from massing an army. Just take down loads of buildings and mob their army while stopping their gold income with towers.

Ulfs are amazing. Its fully possible to have 15 of them by 6 minutes. Most other civs will not have even 10 units to fight you. Use that to your advantage to beat their army (which wont be amde of counter units since no one expects ulfs) and ravage their town. Patrol their base with 2 ulfs to find any new building areas for military buildings. Stop their attempts at making an army before they occur. This is what norse should do and in my opinion the ulfsark is the only unit that can achive this goal.

For Thor and Loki they are also great in the late game. You can get uber bragi ulfs that are made in 5 seconds. This means that there is no way your enemy will reinforce his army more than you will.