mh says wise things. Like him, I am a "traditionalist" and think that properly managed and maintained tape backup offers a lot of advantages (easy to take off-site and offline, low incremental cost to add capacity, "serious" tape technologies (like LTO and DLT) have media that is capable of long-term archival) to disk-based backup alone. Disk-to-disk-to-tape is a great way to shrink backup windows and provide convenient restore, and the cost is typically incremental to tape since a box filled with moderately fast disks (some large SATA disks in a RAID configuration, for example) isn't too costly.
None of your proposed methods mentions taking the backups offline. Backup is both off-site and offline. Keeping your backups online means that an attacker can trash your backups right after they've trashed your production data. It's awfully hard to remotely attack a physical media stored in an off-site, physically secure location.
If you decide to do disk-based backups, I'd strongly recommend regularly taking backups offline and off-site.
Whatever you do, test restoration is in order. We don't do backup to "have backups". We do backup in order to restore. You need to regularly test backups by doing restores. You need to know how to perform restores and you need to perform them on a recurring basis. Your attitude, re: restore, should be "Been there, done that". When a real catastrophe happens the last thing you want to be worring about is learning how to bring your systems back from the dead.
As I said in my comment to mh's answer, online backup is only as good as the restore mechanism (since, again, we do backup to restore). If it'll take 36 straight hours of downloading to bring your data back from the online backup provider and your business can't handle 36 hours of downtime then it's probably a bad deal. That having been said, if you can structure online backups to catch slow-changing "archival" data that's not critical for day-to-day business you can use it as an off-site storage strategy, thus decreasing the amount of business-critical data that needs to be on the physical media that you take off-site.
There are several good questions about this already on Server Fault. I'd go and read them. Here are a few that come to mind to me right off.