First, even though you may urgently need the cash to cover a financial crisis within paychecks, don't grab the first deal you're offered. There a literally dozens of reputable loan companies/providers that want your business; so take charge of your loan application.
If you were looking to buy a new car, wouldn't you shop around to make sure you got the best deal? Why should applying for a payday loan keep any different? So, go surfing a little on the web to check out the loans on offer.
What should you be looking for?
First off, find a lender that will give you the amount you want. Lenders calculate how much they'll loan you on multiple factors. Try a few companies and see what the maximum amount each will give you.
Payday loans really cash advances to help you pay your bills between paychecks. You usually are expected to pay the amount in full next paycheck. If this doesn't suit you, then ask potential lenders if they offer more versatile repayment plans.
Before applying you must feel comfortable that the lender is legit. Things to look out for are: how long as the company been in business (the longer the better); do they have a 'real' address (not just a P.O. Box); do they offer other complementary or free services such as credit reports, debt counseling etc. Another safeguard is to check them out with the Better Business Bureau and the Attorney General's Office. These organizations will be able to tell if the lender has had any complaints made against them.
Finally, determine the bottom line; how much will you have to pay back? Some lenders charge almost extortionate interest rates and other 'administration charges'. Don't be afraid to ask the lender exactly how much you will have to pay back. You can easily compare one lender against another.
If you really want to make sure you really are getting the best guaranteed online personal loan you need to do some investigation and ask some serious questions. Legitimate lenders will have no problems with you doing this and won't pressurize you into making a decision you might later regret.