Short answer: NO . Read on first.
You know by now that your speed seems to differ by the hour, and even
across speed calculators. Why does that happen?
The primary reason is, your internet speed isn't fixed, and does differ by the hour. You might feel like your ISP is pulling your leg at certain hours when lots of people are logged on to the internet at the same time (this article claims the dreaded hours are 10 am - 6 pm in the India; by rule of thumb it's the peak office hours, as well as after hours when all the Net freak in the world are busy socializing.
Different speed tests have different parameters. In case you're aiming to track your internet speed, it's advisable that you stick to any one method. Remember that upload speeds are generally waaaaay slower than download speeds (that's because people upload files much less frequently than they download 'em).
If your PC is attached to a network and someone else is working online, your bandwidth is shared among users. You might be in for some seriously sluggish online moments if the other user(s) are doing download-intensive stuff, such as downloading MP3s or video files.
In case you're up to suing your ISP for not delivering (or deciding to opt for a different ISP, to be more realistic), you should measure your internet speed across different times of the day, and on different days. Compare your average findings to the speed your ISP is advertising. If they're close, be happy and bury the hatchet. Switch to another ISP only if the disparity is alarming. My experience: Major ISPs from the same city, despite their claims to offering the best packages, don't really differ in terms of service quality. And, in case you've been using your email accounts provided by your ISP, switching would mean you have to go through the hassle of moving all your data to your new account, which, more often than not, isn't easy.
Ask people around when you're in an internet speed dilemma. Ask a friend who's using a different connection to measure his/her internet speed (or better, check it out yourself when you're visiting, since friends are by default as lazy as ourselves ); compare the results to your own findings and ponder.
If you're using a good dial-up connection, there's a chance it might still best the newbie broadband in your locale, so you should always check; but if you have a T-1 or better option available in your area and you're willing to dish out the bill each month, hesitate no further. An average ADSL will always be better than a dial-up, and a T-1 will almost certainly beat an ADSL.