Hi I've recently only played multiplayer after quitting campaign on level 17. However, I'm currently on a item/rating gap that I cannot cross over and the multiplayer rewards are not helping. Which campaign level I should do religiously in order to become the top tier player?
I recommend you take 3 dwarf wizards and make a build that looks something like this. Alternatively you can just pack tons of damage (at least one fire wizard). Then finish all four level 17 quest once per day with these same wizards (no build tweaks needed). This takes you less than an hour, and after a week you will have tons of cool high level items that should help you a lot in MP. If you want more variation in terms of gameplay and loot, then I guess the only good option is to redo the whole SP again with new characters, which is surprisingly fun the second time because you are now a "pro". Whatever you choose to do, good luck.
What items do you need? Card Stock and Mauve Manticore will get you level 17/18 items quickly, and many people farm the level 6 dungeons looking for tokenless epics and legendaries.
I agree with all above. And it is nice to farm low level dungeons a bit (5-8 lvl). It goes very fast and some rare tokenless items are really great and even better than 18 lvl ones in many situations. Almost any class could use some of them. Level 16-18 items you will get by playing multiplayer, and they seem more common than low level ones. You can also do challenges for the same reason although it would be safer to get nice stock of items first.
There is no single adventure with "best" loot. There are excellent items of almost all levels. The way it works is the adventures drop items that are close in item level to the adventure level. The spread is something like the below example of 900 dropped items from a level 6 adventure (common brown chests only, the last battle chests give more high-rarity items): Code: Lv C U R E L Tot 3 36 2 2 1 0 41 4,6 % 4 34 5 1 0 0 40 4,4 % 5 184 49 8 4 0 245 27,2 % 6 293 86 18 7 0 404 44,9 % 7 91 36 8 2 0 137 15,2 % 8 7 1 1 0 0 9 1,0 % 9 19 3 1 1 0 24 2,7 % Tot 664 182 39 15 0 900 73,8 % 20,2 % 4,3 % 1,7 % 0,0 % So, the closer the item level and adventure level are, the better the drop chances. The full spread is commonly +-3 levels. If you're looking for items of a certain level, play adventures of that level. ( A warning, though: Trying to farm a particular Legendary item is a fool's game, it's so unlikely to happen you're wasting your time. Even going after one particular Epic can be a matter of a hundred hours of farming or more, not recommended.) You can find lots more info about the loot drop system from the "What is the shortest method to get most gold pieces (gp)" thread.
I'd felt this was the way things worked, but nice job actually proving it. I tend to feel that going for the end chests becomes important once you've reliably filled in your commons and uncommons. The rares and epics you get are often of greater value than the sale price of the lower level items. For example, if a replay an hours worth of the common brown chests, at best I get around 20 of them. With the treasure club that gets me 60 items, that seem to sell for around 150 or so gold and maybe one higher rarity item. In that same time I can also beat around 6 full modules. I expect I'll get at least 2 higher rarity items, plus around 100 golds worth of items to sell. Assuming the random items are rares for sake of comparison, the second method wins out. 150 gold + 100 gold item in comparison to 100 gold + 200 gold in items. But more chances for a higher level item is also preferable once you have most commons and uncommons. For what it's worth, I find that tracking your arcane, divine and martial skills is a good way to see how your collection is coming together. There are no legendary or epic items in these categories, so over time you can put together something like this.
At best I've finished over 30 repetitions of common chest battles in an hour, but I've come to feel that for maximum item gain it's better to do it your way, complete as many adventures as you can. That way you also get a much wider variety of items. I've never tracked the maximum gold gain that way, thanks for the data! I also look at those skills to track the slow filling of my collection. It seems I'm missing e.g. 8 Martial Skills from a full complement at the moment.
