Voting on block producers requires the use of your private key. Voting through websites (with or without browser plugins such as Scatter) or through downloadable applications happens generally when on-line. This makes one significantly more vulnerable for all sorts of hacks. Hardware wallets such as Ledger and Trezor are likely to support EOS in the short term, but until that time it is advisable to generate the voting transaction off-line. We have documented the methodology developed by Tokenika in this video.