After using Mac/65 for about 15 year I decided I wanted to use another Assembler for Atari 8bit. I never thought I would find something better, but i found it in Synassembler. I have to admit: you have to learn some strange directives and other uncommon styles, but after a few hours you are used to that.
This assembler has a few benefits above Mac/65. The first thing is: you can start your compiled program direct from the editor. That is extermely handy, you don't have to jump to dos, or debugger. You write your last line in the editor, you assemble, and you type RUN <addr> and there it goes.
Another benefit of synassembler is: it fits in a standard 8KB cart. You don't need an excotic cart for using it.
Another benefit of synassembler is the "Target File" directive. (See manual)
I have never regret my switch to this superb assembler. It's definately worth a try.