My machine is 10 years old and trying to run new Linux OSs on separate drives requires something else than Legacy bootloader. I am considering going to a new machine but don’t want to endanger the peripherals. So far it all works. I presently have Windows 7 on a SSD but did not try to upgrade to 10. I like the Linux philosophy and it is simply fun. Would it be safer over time to choose uefi or grub2? Presently I am using Linux Mint Cinnamon 17.3 and peripherals work. I plan on sticking to Ubuntu derivatives.
UEFI is a newer version of BIOS firmware that sits on your motherboard. You can choose if you want to boot in UEFI or Legacy BIOS mode. Since your computer is 10 years old I doubt UEFI is present so your computer will automatically boot in “Legacy BIOS mode”. This is good and nothing to worry about.
GRUB2 is a rewrite of original GRUB (Legacy) bootloader. Almost every Linux distribution use GRUB2 these days. GRUB2 isn’t really called GRUB2 but simply GRUB (version 2).
I am not sure I understand your question, just wanted to clarify the differences. 
Thanks for the input. I tried booting Ubuntu Mate from a new download to my drive and was told that legacy is out of date. Same thing happened in Manjaro. The CDs I used were bought from OSdiscs. I want to make sure that if I get a new machine that the new OS of Linux will work.