Any 3.5" SATA hard drive will work. It does not matter if it is SATA I, II or III. Get whatever size you want. You can also use a 2.5" hard drive or 2.5" SSD if you use a 3.5" to 2.5" bay adapter. All that matters is that they are Serial ATA. Given the age of the computer there isn't any benefit to getting a high end SSD. Whatever is cheapest and reliable will max out the old SATA connection.
If you want the computer to work faster use an SSD. As your computer worked fine with 80GB. You could get a cheap 120GB SSD and be good to go.
Any 3.5" SATA hard drive will work. It does not matter if it is SATA I, II or III. Get whatever size you want. You can also use a 2.5" hard drive or 2.5" SSD if you use a 3.5" to 2.5" bay adapter. All that matters is that they are Serial ATA. Given the age of the computer there isn't any benefit to getting a high end SSD. Whatever is cheapest and reliable will max out the old SATA connection.
If you want the computer to work faster use an SSD. As your computer worked fine with 80GB. You could get a cheap 120GB SSD and be good to go.