Generally speaking, the way alchemy works it favors stuff that requires few hits to work well.
The creaters hits - force opposed with a limit on top of that means a lot of high force preparations are going to have 2-3 potency meaning it will even at force 6 roll a mediocre dice pool that is very easy to avoid
unless...
it's an aoe spell
Fireball need no when used to be devastating. No defence (see
http://forums.dumpshock.com/index.php?showtopic=39934 ) and even a full scatter of 6 versus a radius of 6 (on a F6) means you hit your intended target.
It requires a pretty good force to deal meaningful damage (6P, even with AP-6 isn't much) but sometimes the elemental effect (like the -1 dice pool mod and -5 initiative from Lightning) is a good reason to use the spell anyway and you can often do some damage to soften targets for your Sams.
Invisibility don't need that many hits to be useful, same with many buffs. (
Combat Sense,
Armor,
Increase [Attribute]...)
Another spell I love as preparation is Mana barrier.
With the nerf to Counterspelling a mana barrier is even better, it gives FORCE extra dice for spell resistance and has unlimited charges (can be destroyed but...)
[b]Magic Fingers (great for manipulating real grenades near enemies, or to fiddle with their guns or shove a thick blanket in their faces forcing blind fire penalties on them, etc.)
Levitate (emergency parachute, or scale ladders and climbing, remember mages have to dump strength to be good so a way to get around climb checks is nice)
Phantasm Need some hits to overcome illusion resist but the illusion of a drone or raging orc babe with chainsaw hands can draw fire away from your friends (or scare enemies away)
Spells that make very very poor alchemical preparations are things that require net hits to do effect. Direct combat spells, Confusion, Swarm, Agony, Decrease Attribute* and the like
*Decrease attribute is not easy to use, but with touch range it is near impossible to use in combat as it is. A paintball gun firing decrease attribute touch spells can be funny. Decrease Charisma is an extremely powerful incapacitating spell versus all trolls and most orcs. Decrease Strength is hilarious versus all mages (but they tend to resist it).
Also, remember that you can up the effective potency by using reagents. If you build a character focusing on alchemy (6 magic, 8 skill, +home ground and some stuff) That way you can have a F5 Death touch using 12 reagents to deliver a pretty nasty nuke to something. It requires amazing dice pools to pull off. If you can get a ton of hits, you can create pretty funny "land mines" with all kinds of debuffs.
In short, Alchemy requires a creative player. It is easy to do wrong and get weak preparations with abyssmal potency that last shorter than the time it takes to recover from drain and when used the preparation rolls a crap pool and does nothing, leaving the alchemist player sad. With a creative player it can be a very good fun tool for the group.
It is only good in the right hands and that makes alchemy very interesting in my eyes. And it does so without replacing regular spellcasting (because that would essentially make mages into DnD3.5 wizards that have to prepare their spellcasting for the day every morning and can't change their mind once the adventure starts and that would have been super lame)