I see the old HP15c derided by current users by comparing it with HP 50g. They laugh at the specs, the screen size, the programming model, etc. They wonder how mint units can get over 300 € on ebay and other sites.
I have both. In my common work, I use the HP 50g. I can see everything that I have done - sometimes I need to clear to unclutter the stack. However, it is clear to me that it is not a calculator for all purposes: I cannot take it to meetings, or when discussing with a colleague some alternatives, etc. For that, I have in my jacket the HP15c. (For that matter, I could use the HP42s instead - however, it takes longer to navigate the menus and do what you want than on the 15c)
The HP 15c is the unit I take with me in airplane flights, to discussions, when going out shopping, etc. (whenever any of you would make a calculation in your iphones, I'm done long before with the 15c - with the advantage that I can tall the result to the person on the other side of the phone!)
In the past, when there were comparisons with the hp 41c, I/O was a factor - no more (infrared is not often used, since sales of infrared printers are so low, and there are no instruments that can interface with the HP50g, save for the streamsmart model, which is a high school application with no professional instruments to attach.
The programming capabilities of the 15c are more than enough for most business or engineering problems, due to its extense function catalog. There is as well the fact that it will last forever with a set of batteries, while you need to change the 50g batteries every two months id you use it frequently.
If I have both at hand, it's the 50g that I take. If I have a program to do, or solve an equation, it's the 50g I turn to.
I do not want to choose - I want both.
I heard rumours that you will not have to choose, too.