In pvp, poison is probably the best to have as the poison breath can kill players off mounts(be careful though, if you are close enough to the breath it can dmg you, even on the wyvern). On pve poison is the most useless as fire and lighting are more powerful in general. Also poison isn't resistant to fire or lightning breath like fire and lightning are which can result in considerable health loss no matter what wyvern type you are fighting. Lightning has insane range with lightning breath and it does lots of dmg. Fire does lots of dmg over time so if you use the fire along with the bite you can do lots of dmg at once. Also fire wyverns are best for fighting alphas as they are always fire.
To know how much time need to the next feeding just do the next. Look the Food number# then that number multiply x 10, then divide /3600 and the result will be the number of hours until the next time need to be fed. F.E the food number is 1850.5 1859.5x10=18595 /3600 = 5.1 hours
Make sure to stock up on milk and preserving salts. My tribe put off getting milk and had to rush to farm it becasue we got triplets. While you may not be concerned with this, that 2% chance does occur.
A fire wyvern is one of the best you can have because they are resistant to fire damage so alpha wyverns are much easier to kill same with all the wyverns they can't hurt each if they are the same element but the bite attack still works on all wyverns keep this in mind