Back-end: Back-end loads tend to work a bit more in the favor of the investor since they're paid at the end of the investment, based on the initial investment amount. So, that same $100,000 and 5% sales load, but as a back-end, could easily be completely wiped out by the additional compound earnings you make from being able to invest the extra $5,000 until you sell your investment. Sometimes, sales loads can also decrease to zero if you hold the fund long enough.
Level load: With a level sales load, you'll pay a small fee periodically. This might be once a year, for example. These are a lot less common than front-end and back-end sales loads and are also different from mutual fund maintenance fees.
Sales loads versus expense ratios
Sales loads are one type of expense that you need to consider with a mutual fund, but they're not included in the expense ratio. Whereas a sales load is basically a commission to the seller of the mutual fund, the expense ratio is based on other operating expenses without the sales load being included.
An expense ratio represents the annual cost of owning the fund, including things like management fees. It's specifically about money that goes back to the fund itself, so the sales load is not included. The sales load is paid to a separate entity entirely. You will often see mutual funds with both expense ratios and sales loads.