I'm an old HP hold out. I purchased the HP33 but did not like the layout or feel of the calculator. When they released the HP35, I picked one of those up to try. I would recommend it over the HP33 any day. Just has more of an HP look and feel. You can store equations in it such as interpolation. It's not like the HG48 by no means but it has some decent features for the RPN fans.
I just picked up a FX-115ES to try since it has a better equation solver in my opinion. The HP35 will do it as well, but the Fx is just more straight forward to work with. The FX-115ES cost $12.95 at Wally World so it's a inexpensive second calc. Good features for the price. It has a "Math" mode that lets you enter equations as you would write them. Kind of nice for basic calculus work. Just my $0.02