Which is to prefer?

[Nefertem]

I was wondering what to choose.. There is intellect, spell-crit, spell-dmg and the spell-dmg within a specific school of magic..

Now if I were a fire mage with some points in frost or arcane, and had to choose between +spelldmg or +fire-dmg? spelldmg goes for all 3 schools, right? but would I still do as much dmg with my fire spell if I chose +spelldmg instead of firedmg? or does +firedmg increase the dmg done by my firespells more than the general +spelldmg do?

And what about spellcrit? is it important as a mage, or is spelldmg better?

And intellect? that makes you crit more often, yes? also increases the spelldmg if Im not mistaken? so would that be better than to choose a specific spelldmg or spellcrit enchant?

Bastet got quite a few different enchants and Im planning to lvl my mage up at some point, and then which enchants and stats would be to prefer? thats why I filled this post with quite a lot of questions

[TeaLeaf]

Your questions in order:

+20 fire spell damage will give the same damage bonus as +20 spell damage.

Spell crit gives burst damage which means PVP players want as much +crit as possible.  PVE players tend to (but this is preference not the rule) have a more balanced +dam and +crit combo as the lower crit gives lower aggro.  +crit though also increases mana refunds if you have Master of Elements, so a high crit rate is sometimes nice if the aggro doesn't kill you in a PVP raid.

Intellect increases crit rate yes.  At L60 you need approximately 60 intellect to equate to 1% crit.  Int adjusts the crit rate, not base spell damage.  It only increases damage to the extent that you crit more often.

As for which (+dam or +crit), you need to work out what you prefer and take a look at your level, your talent build and remember that spell crit rating devalues as your level increases.  You need about 32 spell crit rating to equate to +1% crit  by the time you reach 70, whereas at 60 this is a lot lower (14 if I recall).  If a spell doubles the damage for a crit you can work out how much 1% is and the compare that to the +dam number.  

For levelling I would choose fire or frost depending on whether you like to nukr and hope they die before the mob reaches you, or get a slower kill and better CC.

One thing not mentioned here which I would recommend is +hit or +penetration enchants or stats.  As you level you will always come across the mob that is higher level than you and on those in particular a spell that misses (remember it's binary, so either the spell hits or misses) could kill you, so I always make sure I am staked up on +hit gear.  As a result my spells miss very rarely indeed and this is way more valuable to me usually than a +1% crit.

TL.

[Nefertem]

Ok thanks a lot TL  :worship:  
Ill use that when I start lvling

[Bastet]

One thing not mentioned here which I would recommend is +hit or +penetration enchants or stats. As you level you will always come across the mob that is higher level than you ....

Also is true for most end game instances, as bosses tend to be above the level you can reach.