forest goblin spider riders VS goblin wolf riders

I think in general wolf riders are better but i remember reading a battle report on a heavily scenery board where the spider riders ability to traverse difficult terrain made all the difference and they won the goblin player the game so in certain situations they can prove more useful

I'd say in previous editions, Spider Riders were better. The reason is because forests, difficult ground, and obstacles were a great impediment to movement. As a result, it was extremely useful for spider riders to be able to move right through a forest, etc.

Since 8th ed. terrain does obstruct movement as it once did, the strider rule is neat, but not extremely effective.

In most cases the +2 movement on wolf riders is superior. However, Spider riders are able to attack buildings with their mounts. A unit of 10 for example can dish out 20 Attacks to a unit in a building with half of them being poisoned.

In fact, the best uses for Spider Riders are in games with lots of buildings, not only are they decent attackers for buildings, but their wall crawler ability to move straight through unoccupied buildings is great.

Like frozenfood said, Snagla adds a different dimension to the unit, but it does raise the cost of a spider rider considerably. This means a unit of 10 Spider Riders with Snagla is 245 points, 275 with full command. That's a lot of points invested in a small unit of fragile goblins.

No it's 10 models, cav cannot use the attacks of the mounts, but Spider Riders can.