Square Top Mountain is really overshadowed by Bierstadt. Square Top is on the other side of Guanella Pass from Bierstadt, so many people just ignore it. Not to mention that the mountain is only 13894 feet tall. Overall, it is much better than Bierstadt.
There is a trail that leads back to the lakes, Square Top Lakes. There is an upper and lower lake, both are easy to reach. The peak looms directly above the lower lake. Take the trail around the lower lake and go about halfway to the upper lake and find a good spot to start climbing. Once you leave the trail, the best way to get to the summit is by traversing directly up the face. It is easily a 45 degree slope, if not steeper. Just keep climbing up the face until you reach the top of the ridge.
Once you crest the ridge, you can peer down on Naylor (private), Silver Dollar and Murray Lakes. All are beautiful and hold lots of fish. The summit is about 0.5 miles west of the ridge and a real easy hike. The summit is rather uninspriing, but the views from the ridge are what makes the climb. If you continue another 0.25 mile west of the summit, you can look down into the basin the holds Shelf Lake (see trip report). We climbed Square Top on June 23, 2001 and Shelf Lake was still frozen and the entire basin was snowed in, quite a sight to see (pictures on the wintertime photo page).
I would have to say climb Square Top rather than Bierstadt. Square Top is a little farther and not quite as high, but there are so many less people. Get to the top of the pass early, otherwise you will have to start from well down below.