Think of litecoin as the change in your pocket, and bitcoin as your large assets and savings. The biggest argument from the bitcoin community against litecoin is that bitcoin’s ability to be broken down into uBTC (fractional pieces of one bitcoin) may render litecoin obsolete.
Litecoin is able to process transactions more quickly than Bitcoin. It offers less time to first confirmation. That may not be terribly important right now given that the market cap is pretty small for Litecoin. But the developers of Litecoin are thinking ahead to when more people are using it to pay for things. As the currency grows in popularity, transaction speeds could become important if people are relying on transfers to clear quickly. Much like how we currently dread when financial transactions drag out, this could be considered a similar situation when dealing with cryptocurrencies: they have to work, and transfers need to complete quickly.
This means that Litecoin has a higher possible transaction volume in the long run. Of course, that would have to mean people are actually using Litecoin for payments. At this point Litecoin is not at the stage where there is much of an economy around it, but that could change. Transaction numbers continue to increase as a result of the spike in Bitcoin prices that has occurred over the last few months.
Litecoin is MAGNITUDES more secure than Bitcoin