Kind of the same, but DS R4 = Wii Softmod isn't a good analogy.
R4: Hardware cartridge which allows the loading of ROMs. I don't believe the R4 overrides very much in the way of DS copy protection considering cartridges are harder to copy/pirate than disc media, but maybe it's just not as well advertised or doesn't seem as big an accomplishment as cracking the Wii (not that I think any less of the DS scene.)
Softmod: Software, modifies and replaces Wii system files and drivers to dupe the Wii's copy protection into accepting homebrew and burned media as legitimate programs.
If you have the time to invest and read up and learn about softmodding, keeping up with updates and new games that need workarounds if necessary, and are pretty confident in your "hacking" skills, then you shouldn't waste the money on hardmods, WODE or chip.
If you have money to throw at the problem and don't have the time to do all the reading and learning that's required with softmods, get a hardware solution.
One thing to consider, is that I don't *think* a DriveKey will allow you to load games via SD or USB, it's primarily to dupe the drive into accepting burned media. (Someone correct me if I'm wrong.) But there's nothing stopping you from installing Softmods along with the Drivekey in order to be able to load stuff from SD.
SoftMods:
+ Can do just about anything and everything (SD, USB HD loading, Sneek, GC)
- No GC USB loading, discs only (unlike WODE)
- Limited to 3X Read on burned discs
- Brick risk
DriveKey:
+ Hassle-free burnt media playing at full 6X read speed
+ No worries about updates breaking your softmods and leaving you high and dry until you fix it
+ Chip firmware updates ensure future workarounds
- May need to keep up with chip firmware updates
- Softmod knowledge/installation still almost essential for other various things anyways
WODE:
+ Hassle-free disc/usb playing with very little softmod knowledge
+ USB HD loading built-in
+ GC USB loading
- Limited to 3X disc read speed
- Relatively expensive