This is pretty tricky as it all depends on the builds you want to play and understanding what works with what - obviously the more you play the better your understanding of this will become…
What I did when I started playing was look at the types of affixes that the builds I wanted to play used… So I’l look at a low life build with Exsanguinous and realise that I need to stack health affixes to get a higher ward… A simpler one would be critical avoidance… every build needs it (well almost every) so I started looking for T5 rolls on crit avoidance…
I also created a filter that shows very rare affixes based on Dammits Item Database… I just put in Very Rare in the search string and used that info find what the rarest affixes for a particular class were and kept those affixed items or shattered them for the affixes… I dont use this anymore as I can fairly easily tell whats good now but it helped in the beginning.
One aside: A lot of people forget about the implicit affixes on items - the ones that the base item comes with… Take for instance the Argent Crest Relic for Sentinels. It can give up to 45% cold/lightning rest without any other affixes which means that that one item has the potential to max out 2 of your resistances… Things like Carapace Shield have 75% Poison resistance… The Bone Amulet 40% physical and necrotic… Gold Ring the same for elemental… Raider Axe for its critical strike. or a Sai with its increased dodge… There are lots of base implicits that can be very very useful… especially when matched with good affixes…
Correct… With forging, each time you add an affix or level one up, you get additional instability on the item which then increases the chance that you will fracture the item.
My t10 rule is based on a lot of crafting to try and get ideal gear - the general gist of it is that I have found that starting out on a T10 item you have a greater chance of getting it to a T18+ or even a T20 when compared to say a T5… This is all because of the added instability of each craft… So starting on a high base item is more likely to get that godlike piece of gear…
Word of warning… Obviously I am mostly looking for end-game level items so my criteria are higher than someone just looking for a good t15/t16 item.
Yes and no… as @Turinqui mentions, the drop instability (calculations were done somewhere on the forum a while back) is usually more favourable… i.e. if you get a t10 drop, its instability has a good chance of being lower than if you took a white item and added 10 tiers to it via crafting… In direct contrast to this… the missing affix slot IS sometimes not a bad thing - i.e. lets say your really need an item with 2 x T5 of very specific of affixes for your build and the other slots are just icing… Its easier to get the maxed out tiers on the affixes that you want if there isnt a forth affix… again its just the instability factor…
Blue items are sometimes pretty good - I would not ignore them entirely i.e. use a lootfilter. … Sometimes a blue item with only 2 affixes can have a very good roll .e.g. 2 x t5… and if these affixes are what you are looking for, then this can be a good base item to craft on…
My last lootfilter rule highlights anything with one T5 affix - that way I can always see if any item is worth a quick check… Obviously if the lootfilter allowed for it, I would have it highlight any item with a total t10+ but it cannot do that right now.