Get ctags in vim to go to definition, not declaration

I think that the easiest way is to use "g ctrl-]" instead of just "ctrl-]". If there is only one match, it will take you there. If there are multiple matches, it will list them all, letting you choose the one you want, just like :tselect. The best of both worlds. :)

I believe Vim goes to the first tag in the tags file by default. You can select a different one if you prefer: use :tj (similar to :tselect, but auto-jump if there's only one match) or Ctrl-] followed by :tn).

The only way of changing the default is to change the order of the tags file, but I don't believe ctags offers a command-line option to do this.

This isn't as hard as it sounds as you basically need a script that opens the tags file, sorts it by the 'kind' of tag and writes it back out again. The 'kind' in the tag is a single character describing whether it's a function (f), a function prototype (p), a macro, a enumerated name etc etc etc. If you're using Linux, it could, in theory, be as simple as:

#!/bin/sh
ctags -R -f - . | tac > tags

Since tac reverses the order of lines in a file, this will automatically put the definition first. However, it gets a bit more complicated as the header needs to be maintained and Vim prefers the tag file to be sorted, so it's better to go through the file and sort on the first entry (the tag name) in forward order and then the kind in reverse order. Therefore, something more complicated may be better.

I apologise for the shameless plug, but I have written a Vim plugin that (indirectly) does what you need. It is intended for adding lots of extra highlighting groups for things like function names, macros, enums etc. However, one of the other things that this does is re-sort the tag file so that the function implementation comes before the function declaration, thereby achieving what you want (I had the same need as you). If you don't want any of the highlighting functionality, you could probably strip it all out quite easily: it's a fairly simple python program and an even simpler Vim script and is available from my site.