What mana fixing should I use in Khans of Tarkir Sealed Format?
Mana fixers can virtually never be counted as full lands because you need mana to cast them.

Let's take the case of the banners specifically. If you swap out a land for a banner, the main difference is the banner:


Costs 3 mana to cast
Can be sacrificed for a card draw


(1) makes them a higher mana screw risk than a land (how happy are you if you mulligan into 2 land+banner instead of 3 land?), while (2) makes them a reduced mana flood risk than a land (sac them if you have nothing better to do with your mana).

They should almost certainly be counted as full spells for purposes of mana ratios, especially if you're also playing lands that come into play tapped.