twoopt package fulfills your needs there is nothing wrong with using it...
In general LaTeX is a constantly developing system. Packages are the engine of this process. By neglecting their usage universally or choosing to hard-code if there would have been a suitable package, you would refuse an important property of the LaTeX system.
Although the last statement sounds a little dramatic, there is truth in it. Apart from that, often it remains a matter of choice and habits (we are all humans!). But, if you have the opportunity to obtain a more readable code through package usage, go ahead. This criterion is, by the way, a major issue of the LaTeX3 project.
Being bound to a package in a
.cls file is not limiting you in any way. Even if a package you used in your own package code will be deprecated in the future because of a newer package being better or whatever, it does not mean that the feature you used isn't viable anymore. Moreover, as a package writer you can maintain/update your package according to the state of play. Besides that, I'd like to recall the fact that LaTeX2e is very stable at the moment. So, "[using] the official stuff" (@Sean Allred, see above) is totally reasonable from this point of view.
And finally, if three packages do the exact same job for a particular issue, i refer to the above statement "we are all humans!": Use the one you like best or the one you are used to.