does it matter if you choose to imbue an ethereal great maul or an ethereal thunder maul - regarding possible outcome?
is it more likely that a thunder maul gets a high %ed for example, than a great maul. i'm wondering if it's just as good imbuing a great maul and upgrade it should it be a good imbue, since they are alot easier to find than eth thunders
A thunder maul is an elite item and thus has a higher base quality level which has a positive influence on the maximum affix level, but as long as you are imbuing with a high-level character, it won't matter. However, if less affices are available, those which are possible have a higher chance to appear. For example, if there are only 10 affixes possible because of item level or base quality level and the desired one is among them, you will have a higher chance to get that affix than for an item with a higher item and/or base quality level. which will have a broader selection of possible affixes
That means, for the optimum chance you have to make sure that the affix level (which is calculated from the item level ande the base qlvl) is as low as possible while all desired affixes are still possible. Instead of doing that math by hand (the formula can be found somewhere in this forum), you can use this affix level calculator.
Base quality levels are a property of the base weapon, you can find a list here: http://diablo2.diablowiki.net/TC_1.10. The qlvls of the unique and set items are something different, the monster level also has to be at least that to produce a unique or set item like that while base qlvls are used for calculating the affix levels of magical and rare items.
The item level is equal to the monster level. You can find a list in the Strategy Compendium, a link is in my sig. Random bosses and theoir minions have a +3 bonus while it's +2 for champions.
The qlvl of the item is just one of the variables which decide about the possible affixes. Another is the ilvl (and the magic level, but it's 0 in this case and thus irrelevant) which is charlvl+4 when imbuing, as Ragnarod said. Play around a bit with the affix calculator mentioned in my first posting to find out the optimum ilvl for imbuing.