Instant Pyroclasm is awesome, although uncounterable isn't always relevant (but fantastic when it is). I personally like Fallout because a lot of RDW creatures like Keldon Marauders and Stormblood survive it. There are also a lot of X/2< in standard like Bob, Bloodbraid, tokens, manadorks etc.
A lot of Mordern creatures are merited as being 'beyond Bolt range', and therefor beyond Slagstorm too. I don't find Slagstorm as versatile when we already have Bolts and Incinerates. The difference between 2 and 3 damage isn't really enough of a selling point for me to switch from Fallout, because you need a way to deal with, or push past, anything with 4+ toughness anyways.
Pretty sure slagstorm is a worse version of flamebreak. If you're playing online, counter spells probably are less than 15% of the meta. So flamebreak is probably better.
The colours are more restrictive, but Firespout is probably better than Slagstorm. I think Volcanic Fallout is the better choice overall, though. Instant speed, uncounterable, kills 90% of the things Slagstorm would kill.
Watching the GP Columbus stream, it seemed the instant speed of fallout was what really made it shine. I didn't see anyone running other red sweepers, although I wouldn't be surprised to see Firespout in a RUG Delver deck.
Which is better in what situation? Does it depend on your deck or your opponents deck?
In the current meta what would be the best sideboard answer? Is there even a right answer?
Experimental Kraj
A lot of Mordern creatures are merited as being 'beyond Bolt range', and therefor beyond Slagstorm too. I don't find Slagstorm as versatile when we already have Bolts and Incinerates. The difference between 2 and 3 damage isn't really enough of a selling point for me to switch from Fallout, because you need a way to deal with, or push past, anything with 4+ toughness anyways.
http://www.mtgo-stats.com/stats/Modern
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Decks I play and stuff.
Legacy Burn
Modern Mono U Tron
Legacy:
UR UR Delver
UBR Ad Nauseam Tendril
W Death & Tax
Modern deck:
UW UW control (with Spreading Seas and Wall of Omens)
BRG Vengevine!