First, it's important to distinguish between a BIOS-mode installation and an EFI-mode installation. Most computers sold until mid-2011 used BIOS firmware, which means that they necessarily use the BIOS version of GRUB or some other BIOS boot loader. Beginning in mid-2011, though, manufacturers began switching from BIOS to EFI (although most confuse matters by using the acronym "BIOS" to refer to their firmware). EFI-based computers use EFI-mode boot loader natively, although most of them can also use BIOS-mode boot loaders (often called "legacy-mode" or "CSM-mode" in this context). With the release of Windows 8, most computers now boot Windows in EFI mode, although if you've removed or re-installed Windows on such a computer, all bets are off. See this page
for information on how to determine your boot mode. Understanding this detail is important because your boot mode determines the boot loaders you can use, and to some extent how they're configured.
Second, if you boot Linux, you must
use either GRUB or some other Linux boot loader. (Versions of GRUB are available for both BIOS and EFI.) Mint installs GRUB 2 by default, but if the installer detects no other OS, it may set the default entry to boot Mint with a timeout of 0, so you won't notice GRUB working. If the installer detects another OS, or if you've got multiple kernels, chances are the timeout will be set to a higher value (I don't recall what the default is, offhand), so you'll see a GRUB menu.
Adjusting GRUB defaults can be tricky because they're spread across various files, which are then read by the "grub-mkconfig" or "update-grub" scripts and assembled into the actual GRUB configuration file (typically /boot/grub/grub.cfg, although it can be elsewhere with some configurations). The most notable GRUB configuration files are /etc/default/grub and most of the files in the /etc/grub.d directory. (Note that's /etc/grub.d, not /etc/grub.) The /etc/default/grub file holds the default entry and timeout values (GRUB_DEFAULT and GRUB_TIMEOUT, respectively).
In some cases, it makes sense to abandon GRUB 2 entirely in favor of another boot loader or boot manager. This is especially true if you're having problems getting GRUB 2 to do what you want -- it's finicky and difficult to configure beyond a few basics. On a BIOS-based computer, GRUB Legacy, LILO, and SYSLINUX are all alternatives. They're all simpler and easier to configure "from scratch" than GRUB 2, but because they aren't integrated as tightly into Mint as GRUB 2, these alternatives can actually be harder to set up -- you'll need to do stuff manually that's done automatically by support scripts for GRUB 2. Under EFI, a patched version of GRUB Legacy, ELILO, SYSLINUX, gummiboot, and rEFInd are all possibilities. Of these, rEFInd is likely to be the easiest to set up, since it scans for bootable OSes and creates a menu dynamically rather than relying on a configuration file to spell out every detail. The others, like the BIOS alternatives, are easier to configure than GRUB 2 in a theoretical sense, but in practice the fact that Mint explicitly supports GRUB 2 can make it easier to use -- until something goes wrong with GRUB 2!