There's a few other variables besides Ilvl involved. You have to wear the correct armor type for your class or you you'll lose stats. For example, if you're playing a lazer pigeon druid, you won't be able to just equip the highest ilvl engineering goggles and gain stats from them because they're cloth.
Another variable is how weapon speed effects certain classes/specs but doesn't effect others (like WW monk). A ret pally would use the slowest 2hander available and that would be BIS instead of just the highest ilvl weapon. For casters it's wands over every other weapon. Wands seem to count as two slots instead of one, at least that's the hypothesis of several people in the community. With wands just go for the highest ilvl available. Wand speed doesn't matter.
Fair warning though; a major patch just went out and many things inside instanced PvP are not working as intended. I recommend keeping an eye on patch notes and updates right here on this site before playing any games. I believe gear and consumables are still bugged, but I've been staying away from low level pvp because of the bugs so I'm not certain.