The best tool for the job is the tool that gives you the results you need with as little effort as possible and as quick as possible.
There are so many considerations: do you want error checking on your input, are you going to use the setup regularly, will there be a lot of changes in the way you are going to process your data?
And, even though you can do a lot of the same things in either program, the question is … questionable.
Excel excels in its multitude of very specific functions. Some are available in Coda, and if they are not, you can build them yourself. Excel is extremely flexible when it comes to organizing your data - all on one page, on different pages or in different files - to be connected by formulas at will. It can get messy in a hurry, but in the right hands, it is extremely powerful.
One of the biggest drawbacks in Excel is that you have to copy your formulas, thousands of times and when you change a formula, you have to do that again. Fortunately you can do that for the entire column, without knowing in advance how many rows the column will eventually hold, but it will always be a multiple step operation. In Coda, you change a formula and it applies to all rows right away, which is really nice. With the copy and past actions in Excel, a mistake is easily made and easily overlooked.
For many jobs, I would be tempted to say that Coda is a better solution, and even more so in a multi-user environment. Building complex formulas is a lot easier in Coda then in Excel, and really so if you have to use VBA - which is pretty hard to master.
But there is also a matter of scale: I you have Excel sheets with a couple 100K’s of rows, the choice between these two is easily made: you have to use excel. If you need real advanced charting or mapping functions, it is also going to be excel (for now, that is).
But for the majority of jobs (planners, to do lists, organizers, address lists, calculations, etc.): if it fits size-wise in Coda, you are most of the time better of on Coda. I have been a spreadsheet junky for years, but these days I can build better and more robust multiuser docs/worksheets/apps in Coda. I can organize my work better (a 100 sheet Excel doc is not very workable, a 250 page Coda doc can, with some proper organizing, be perfectly manageable.
So, going back to the title of this thread: Coda is very often more practical then Excel, but each program has it’s own merits.