I play Twin Bolt over Touch, there are too many threes and the deck only had two Stranglers. Bolt is almost always better.
Bolt is never better vs Myr.. or as a finisher. It's good early to get some 1-2 toughness butts out of the way.. which is a significant advantage.. but it's value falls off after the early turns. I really, really hate losing a Forerunner of Slaughter to a Perilous Myr.. It's such a huge tempo loss for you.. you don't even want to attack into it and you're likely to get 2 for 1ed. Before you ask how often I see Myr.. I'd tell you it's about 1/3 of my matches. All the folks without the cards still run it, Crats runs it, Gruul/Evoleap runs it, Thopters run it.. It's still out there. Touch also kills Jaddi Offshoot/Chief of the Foundry/a bunch of other 3 toughness annoyances which your only answer for is Exquisite Firecraft/Ob Nixilis or two-for-oneing yourself.
I'm also not going to succumb to the curve argument. This is essentially a good stuff/burn deck and I want the best stuff and the hottest burn. Also.. Twin Bolt isn't a card you factor into your curve IMO.. its not a card that gets played on curve.. your creatures are what matters in the curve.. how you build your board.
T1 Sludge/Thornbow
T2 Myr/Forerunner/Bear
T3 Aggregate/Dominator/Strangler
T4 Pia and Kiran/Dust Stalker
T5 Win
Where does Twin Bolt fit into that equation? It's not a curve-out card.. It's spot removal.. and often times you won't be able to advance your board anyway.. regardless of which one you've cast.