Depends on what level campaign you're running. If the campaign doesn't plan on going past level 10, definitely Snowball. If you're going higher, then you might consider picking up the Reach Spellstrike Arcana (at level 9) and using Frostbite. It gives you one attack/Caster Level, and does 1d6+CL damage, meaning you cast it once at level 10 and the next 10 arrows do an extra 1d6+10 damage. Because of this, your overall damage with FB will definitely outclass Snowball, even if it's intensified, empowered, AND maximized, and it continues to scale as you go up. Also, if you pick up Heighten Spell, you can use it as a higher DC spell and add on Dazing, Rime, and/or Toppling Spell Metamagic on it. It's a pretty nasty combo from level 9 on. Don't forget Spell Perfection, too.
So Intensify actually doesn't work with Frostbite. It only works with Snowball, Shocking Grasp, Fireball, and other spells that scale +1d6 per caster level. But thankfully that's actually not too big of a loss.
If you focus on Frostbite, you can save the feat for something else, like Point Blank Shot, Dazing Spell, Spell Focus, Mage's Tattoo or others.
Some thoughts, though.
2. Cyclonic: With a Cyclonic weapon, no amount of wind or water will keep your arrows from hitting. And GMs love casting Fickle Winds to negate archers. Put this on your bow so all of your arrows (specifically your spell-storing ones) benefit from this. The +2 Enhancement cost is worth it, trust me.
3. Seeking: An elegant enhancement at only a +1 cost. Negates miss chance from concealment/total concealment as long as you know which square your enemy is in. Remeber GM's love using concealment, too. Put this on your bow.
4. Adaptive: Doesn't matter if you are a Dex or Str character, get this. If you get enlarged, you want your bow to scale your damage. If you take a negative level or str damage/drain, you want to be able to still fire your bow. A steal at only +1000gp (which doesn't factor in to the +10 enhancement limit). Can only be put on your bow.
5. Impervious: Getting your weapon sundered sucks. Getting your bow warped or broken by magic/nature sucks. Get this. +3000gp (also doesn't count towards enhancement total). Put it on your bow.
6. Holy: This one is optional, but if you're good (most campaigns are), and you're consistently facing off against evil opponents (most campaigns do), then this might be worth a look. +2d6 damage/arrow is awesome, but the +2 enhancement cost is kind of annoying. It's up to you. If you get it, put it on your bow.
7. Ghost Salt Blanch: For only 200 gp, you can turn 50 of your spell-storing arrows into Ghost Touch spell-storing arrows, and do full weapon damage vs. Incorporeal creatures. Seriously balls-to-the-wall awesome as a utility/back-up.
1. Frigid Touch (Level 2; 4d6 Cold Damage; Staggered with no save) Make sure you fire at least 1 per round, as the stagger only lasts that long.
2. Mudball (Level 1; Blinded no initial save)
3. Vampiric Touch (Level 3; 1d6 Negative Energy Damage/2 CL; No save; Possibly heals you whatever it takes from your enemy (but don't count on that, it's a pretty gray area))
4 and 5. Fireball and Lightning Bolt (Level 3; 1d6/CL; Reflex half)
I'm sure there are more, but these ones are pretty basic and they're all on your spell list.
Of course you don't have to do any of this. This is just a suggestion. You could take Intensify Spell and focus on Snowball still. It's an awesome spell in-and-of-itself, and with the right traits (Like Magical Lineage and/or Wayang Spellhunter (which stack, btw)) and feats (Like the godly Spell Perfection), it can be a Dazing Intensified Empowered Rime Snowball for ~15d6 damage at a level 3 spell, meaning that you can put it into your spell-storing arrows as well and hit really freaking hard with every arrow. And, you can do this trick from level 1. Just make sure you have Elemental Spell or a Rod of Elemental Spell so you can deal with different types of energy resistance. (But you should have that, anyway.) ;)
The downside of Snowball is that it takes up quite a few feats and its save DC's are going to be less than if you bump Frostbite. Ultimately it's a powerful tactic, though, and it can still be used with Rime spell, too.
That's why I personally prefer Frostbite, because you don't have to take a bunch of other feats for it to be really effective, and you can use Heighten Spell to raise it to a level 6 spell (increasing its Dazing DC), a lot easier than Snowball, plus it just keeps giving and giving.
If you like, I can post more in-depth samples for both/either build so you can get a detailed idea of what to expect. I might post another spoiler section about various items that can help you, too, if you want it.
Cheers. :)
P.S. Sorry I realize it might seem like I'm patronizing you. I just wanted to make sure everything was as clear as possible for any posterity looking stuff up in the future. :)
WombattheDaniel,
Thank you so much for your detailed suggestions.
Some of them are great!
Unfortunately, spellstoring is an ability that can only be applied to a melee weapon.
Even if spellstoring could be added to an arrow, it would have to be a +1 arrow first, which makes it a very expensive arrow since adding spellstoring would make it a +2 arrow (so 8,000 gp for 50 arrows).
I do plan on using some of your ideas. I didn't even know "cyclonic" existed as a magical property.
Quick hijack; Wombat, in your opinion, which path is better for a magus, str or dex?
Edit: for a melee magus, not the archer.
It's a very hotly-debated question, but it's one that I've researched pretty heavily.
Both are very good for their own reasons, but, short answer, I think that Dex ultimately gives you more. With a Dex=Int>Con build, you only have to really focus on those, so you are a good deal less MAD than a Str=Int>Dex=Con build.
Dex is a godly ability. Initiative, Reflex save, AC, and with the right specializations, it can be to-hit and +damage. You just get more bang for your buck at the cost of (depending on your build) 1 feat. And the Magus already gets 3 bonus feats, anyway.