Hi,
I use Net::SFTP::Foreign::Backend::Net_SSH2 which (as you may have guessed) uses Net::SSH2 for the sftp transfers.
I find it very good, though I don't think I've ever had to transfer anything bigger than about 10 megabytes.

I used to transfer using scp via Net::SSH2, but sometimes experienced incomplete transfers. However, I think that problem (in Net::SSH2) has since been fixed.

Cheers,
Rob