It depends on whether your database will be mostly reads, mostly writes, or an unknown mix.
If the database will be mostly reads (SELECTs), then go with all eight drives in the same RAID 10.
If the database will be mostly writes (INSERTs/UPDATEs/DELETEs), then you might even want to consider two 4-drive RAID 10 arrays - especially if your databases will be doing frequent transaction log backups, database mirroring, or log shipping.
If you just don't know, I would go with 2+6 if the server has space to add additional hard drives in the future. That way, if you decide you need more performance on the data or log arrays later, you can usually hot-add pairs of drives and restripe them without an outage. If you post the RAID card model, we can check that for sure.
If you don't know, and you don't have space to add additional drives, then I'd go with a single 8-drive array for easier management. You won't be as worried about running out of space on the log drives.
And no matter which option you choose, put the log files on a separate logical drive from the OS. If you suddenly have a ton of transaction volume and the log files fill up the OS's logical drive (C), your server can go down hard.