I do things on different computers and platforms (mac, windows, linux) so I've pushed my customisations into the bash layer more than the terminal apps. To more directly answer your question - actually I just use Terminal on OSX.
The main niggle I have with OSX Terminal is that it runs Bash v3 and not v4 (and Apple advised on a support ticket there were no plans to change that in the foreseeable future); and iTerm also runs v3 at least out of the box. It's not a massive issue but it does occasionally bite me writing shell scripts.
If you're really unsatisfied with Terminal you should probably consider alternative shells (like zsh, csh, fish, etc) as well as alternative terminal apps.
The upside of deeply customising your workstation's terminal+shell is you can tweak to the absolute nth degree and access really powerful (non-standard) shell features beyond the stock set available in bash.
The upside of sticking to bash is it's the currently the de facto standard, so when you encounter a new system things will probably be familiar. Bash is the default shell for...
All of that said - and I appreciate it's a lot ;) - I am not at all saying that you shouldn't use iTerm or try alternative shells. I just don't have enough pain points with default bash to outweigh the convenience of consistency across systems.