This post will continue on what I talked about in earlier discussion about the Wyvern in O&G armies. Previously I've brought up a few tactical options and uses for the large monster in hopes of countering the negative view shared by many, that considers the wyvern ineffective for its point cost, and in general too weak to accomplish what you as the general hope to do with it. This time, I'll provide some answers to two common wyvern questions.
Who should be riding it then?
We have two choices here, which both have their merits. The first and most popular choice is to have a Warboss riding it, meaning it'll be far more potent in battle but also means our general (and his leadership) will be flying around far away from our infantry, which can become a problem. On the other hand, the Warboss should be able to take out soft to medium units on his own, and will be an excellent rank-breaker for our hard hitters. With the Warboss riding the wyvern, it's even more important to have a fast army to ride with him and benefit from his leadership. Most cases whenever I create a list I tend to favor a Black Orc as the general, but that's mainly because I feel the most important attribute of the Black Orc is his ability to quell animosity in the orc boyz he's leading. Since the Warboss will be on his own, away from a unit, I see few reasons to pay 28 points more just to get heavy armor instead of light, an extra point of WS and the ability to use a non-magic great weapon (that you won't get full bonus out of due to being mounted). The Savage Orc can be great, but better reserved for when their charge range is a more manageable 14" (on a boar or in a chariot). Having a 500-point frenzied flying monster with a charge range of 20" is just asking for it to be baited and killed. So in my opinion, the regular Orc is the best choice to ride the wyvern. In fact, this is one of the few occasions where I feel the regular orc warlord has a place in the army.
The other option is to skip the Warboss entirely (unless you're playing a massive 3000+ point game) and instead have a Great Shaman ride the wyvern, while having a Big Boss lead the rest of the army from the infantry. It'll mean one point less in leadership, but at least you'll have him providing a firm hand for the rest of the army, from safely tucked away in an infantry unit. This setup does not necessarily require as many fast moving units to be effective, as the shaman will be just as happy flying around and getting in good positions to destroy the enemy with spells and scaring nearby units than he would be in combat (something he will struggle with). This mean that you can field a wyvern and still play to the main strength of the O&G army: gang up on the enemy with hordes of infantry blocks and smack them in the flanks with your hard hitting hammer units. Even with magic items, the shaman will be easier for the enemy to shoot down, so more care must be taken when you place him on top of a wyvern. On the other hand, he will not be as concerned with getting the perfect charge in, and should still be able to get into good positions for his spells while keeping away from shooting units. With the help of the wyvern, it's possible to still take out fast cavalry, some skirmishers and war machines, but you definitely need to think twice before ramming him into the flank of a nasty combat block considering you'll only be swinging four attacks at the enemy.
How to equip the rider?
Whether you go for the tough Warboss or the powerful Great Shaman, I would equip my rider with Warboss Umm's Best Boss 'At every time. Considering that you'll most likely be the prime target for enemy shooting, some of the artillery pieces that allow no armor saves were they to hit you, the +5 ward save becomes really important. Normally, I'd say that a +1 or +2 armor save should see your general safe through the battle as long as you keep him in a big unit, but when it comes to your wyvern rider, I believe the ward save is an excellent option that (dice willing) will ward off artillery hits no matter how much they hurt.
For the Warboss, I would further equip him with Ulag's Akrit Axe, an Enchanted Shield and either Bigged's Kickin' Boots or Warboss Imbad's Iron Gnashas, depending on the opponent. This will have him dish out 4 (or 5) S6 attacks on the charge with re-roll on the warboss' misses and killing blow (alongside the wyvern's 3 S6 attacks), while granting him a +4 armor save next to the ward save. The armor should keep him fairly safe from regular missile fire, while the re-rolls will hopefully ensure that not too many enemies can strike back on your fragile (considering the cost) general. In most cases I would favor the extra attack over killing blow, since it will probably be more useful more often, but there are times when you go up against that heavily armored opponent that won't even be scared of the S6 hits, where you'll thank the killing blow for ignoring the armor save. I believe that you should outkit your warboss so that he will be as solid as possible as often as possible, as I believe that's the best option for what he is supposed to do. It is certainly possible to make him more dangerous in combat. If you're lucky with Guzzla's Battle Brew and make him a frenzied, hating orc, then give him Shaga's Screamin' Sword and drive within range of 4 enemy characters, you can be dishing out 9 S9 attacks on a good day (+ 4 S6 attacks from the wyvern) with both re-rolling their misses, but those days tend to be so rare that I don't think it's worth it. He's enough of a glass cannon as it is, so I would always recommend more solid equipment choices.
When it comes to the Great Shaman, there aren't that many good options available. The Idol of Mork is too expensive for what it does and requires the army to consist of many large orc blocks in order to be worth it. The Staff of Baduum adds +1 to any casting attempt by the wielder, which is an alright option especially if you plan on casting a lot of minor spells to pierce the enemy magic defense. Both the Skullwand and the Waagh Paint is better used on a shaman more interested in close combat (such as a savage orc). In the end, I would probably go with Nibbla's 'Itty Ring, since the ward save makes him the ideal carrier (on a roll of '1' you take a S5 hit with no armor save) while the extra 'eadbutt spell is great. Depending on what other shaman characters you're running, I would then consider just stocking up on 2 dispel scrolls for the remaining points, since the other level 2 shamans may already be packed with useful items for them and unable to stack up on scrolls. Alternatively, you could get your Great Shaman a pair of power stones instead.
All in all, the wyvern rider can be a great addition to the Waaagh! if not vital to its successes. It gives you as the general a few cool tactical options that aren't normally available to greenskins. It will struggle to earn back its points, and will need to work together alongside other units to really be successful. In order to have it survive long enough to do that, however, you need to protect it, both by magical items but also by good positioning during the match. Hopefully some of the points I've made here will help you do that.