If you are using the HDMI output, both the BDP-103 and the BDP-105 will give you the same picture and sound. The BDP-105 has a couple of extra features, and a reworked audio section for the analog audio outputs.
Now, the Darbee versions of each simply adds the Darbee processing. The question for you is whether you want the processing or not, and whether you are willing to pay $100 for it. I personally would not want it. Some other people would. It is really a matter of personal preference.
To help you decide, you can look at the effects of the processing on the Darbee site, to which Oppo has provided a link:
Gallery DarbeeVision
Look at the processed pictures, and compare with the unprocessed, keeping in mind that they are tying to sell you something. If you like the processing and are willing to pay $100 for it, then it is worth it to you. If you don't like it, or don't think it is worth an extra $100, then it is not worth it to you.
Here are a couple of articles that you might want to read:
Darbee, yes or no:
In summary, if you are looking for a quality player that accurately reproduces video, the BDP-103 is the right choice; if you are looking for a more customized experience beyond standard picture adjustments, the BDP-103D provides additional possibilities to fine tune your viewing experience.
OPPO Digital - Knowledge Base
BDP-103 vs. BDP105:
... the BDP-103 and BDP-105 are identical in performance when it comes to audio and video over HDMI ...
OPPO Digital - Knowledge Base
The one article is about the question of whether you want Darbee processing or not. The other is about whether you want to go with the BDP-103 or the BDP-105. If the one convinces you that you want the processing, and the other convinces you that you want the BDP-105 instead of the BDP-103, then you want the BDP-105D. If it were my money, I would go with the BDP-103, and forget both the Darbee and the enhanced analog, as I would not be using any analog output and I don't care for the processing. Other people would use the analog outputs and feel differently about the Darbee processing, and so they would choose according to their preferences.