I just went through an "upgrade" of my drill press about a month ago. Im just a DIYer with home, car, and basic furniture projects. (i.e, redo a backyard deck, car maintenance, make a painting easel for my daughter etc...) so... IMHO ...
based on what I see regarding that 10" press, I would say that it would be able to drill a 1/2" hole in medium steel if absolutely necessary. I've done 1/2" holes at 700 rpm. Used lots of lubrication, went slow, and still smoked my bit at times, but it got done. If I needed to drill 1/2" holes often, I'd look for something with a low end speed down in the 400ish rpms. It should drill wood holes easily except for perhaps the use of hole saws. Of course, the largest width of project would be 10". For me, the physical size of my wood projects are in general bigger than my metal projects.
That second 15" press you listed is a much different beast. Im thinking it'll do 1" holes in steel pretty well. Obviously, since it's taller and bigger, it'll handle much bigger sized projects.
My guesstimation based on my recent CL search in SoCal, is that the 10" press would be found around $50-75. The 15" Press has a bigger range, maybe between $150 and $300.
Of course, I agree with others, an older press would be more durable and come with some character. In that case, you need to have more patience to wait (they're often not only old, but beat up) - have some more cash to pony up (good condition or already refurbished) - or have the time to refurbish something up to your standards by yourself (yeah, ok, I can buy it for $100, but will spend $200 fixing it up over the course of 6 months trying to find parts).