Either is okay with me. Be generous, give the condemned a choice. I don't see why we couldn't go a bit more sci-fi, though. An remotely-activated version of the Futurama "suicide booth" would work. Or one of those big lasers that we spend megabucks developing but never turn into a viable military weapon. Zot!
Actually, i think the Biblical method of stoning is best.
1. It works to foster more moral certitude of those doing the stoning. It i one think to allow the state to do the dirty work, but like welfare, it fosters ambivalence, whereas if you do the stoning, you want to make sure the one being stoned is guilty.
2. It provides a deeper sense of justice for Boston Marathon fans to stone Tsarnaev (not that many would, unlike Bruin fans) than the state to do so.
3. It forces the criminal to see the corporate nature of his/her crime.
"Thank you for using stop'n'drop. Americas favorite suicide booth since 2008. Choose between quick and painless and slow and horrible."
"I'm sorry we are out of quick and painless. Please select another option."
A bit messy, though. But it should satisfy all "cruel and unusual" arguments. IMO