My preference would be to go for individual files, whose names include the date and time of the backup. Advantages being:
1. If you look at the backup directory, you can see at a glance which backups you have without having to go to msdb or the Enterprise Manager GUI
2. If you’re short of space in the backup directory, you stand a better chance of freeing enough space to continue, while keeping recent backups on hand in case you need them, if you have a large number of small files rather than a small number of large files.
3. If you have problems with a particular backup, you only affect the one file.
By the way, the Maintenance Plan setup wizard defaults tran log backups to have a .TRN suffix rather than .BAK; you might like to consider something similar to differentiate between your full and tran log backups. If you’re forced into doing a recovery in a hurry, anything which clarifies what you have to work with is good!