Opera 12.18 for most sites (including this one) and Mypal for the sites that Opera is starting to have problems with. It's a solid combo, particularly for older PCs (I'm using a 2.8GHz Pentium 4-based PC, an HP Compaq DC5000 SFF with 4GB of RAM [upgraded from 512MB] and a DVD+/-RW drive [upgraded from a basic CD-ROM [not a burner]).
I mainly run older software on my PC; most of the program versions I use will work with Windows 98SE, and in some cases even with Windows 95. This makes a big difference on older hardware, especially when you're relying on on-board graphics and an old 40GB HDD and don't have a dedicated graphics card or an SSD.