Well, it depends... (only vintage gives the true lo-fi grit, but you probably know that already) D-05 gives you a lot of presets (if you can stand them) and the size is unbeatable. The Roland Cloud D-50 vst also sound spot on - low bitdepth and all - but at the moment you have to agree on Rolands cloud business model and I don't.
The D-50 (and D-05) has an earlier (1st gen), more convulted version of LA-synthesis. Sound parameters can be found all over the the place and it is "messy" but gives you the most of possibilities for transforming the sound, more LFO´s, EQ and FX. D-50 and D-05 are only monotimbral. (There was an expansionboard for D-50 that made it bitimbral I think, but it is rare)
For the 2nd gen (D-110/20/10/5) Roland simplified and reduced the amount of parameters (the only LFO here is a joke and only affects pitch), they included more samples (TR-707-style drumsamples that can be edited!) and added some more "structures" (the basic set up between oscillators & ringmod). If you use a D-110/10/20/5 in multitimbral mode everything is much more collected and straightforward. IMHO it is a lot easier to navigate this architechure even though some parameters are "missing". It makes sense in a way because you are using more sounds for arranging a track anyway. (Some D-50 sounds are more like one track of its own, like the Wavestation presets... They can sound cool but are hardly useful and sounds very dated.)
So, I would say... D-50/D-05 for the full "original" LA-synthesis and D-110/20/10/5 for digital Lo-Fi track experiments/compositions.
If you just go "outside/beyond" some of the regular settings for the D-series synth parameters there is a lot of fun stuff you can come up with. The drumsamples in the 2nd gen are invaluable I think since they can be edited and combined beyond recognition. (the beats on autechre's "Djarum" sound totally like the stuff I used to do on the D-20. For a long time I only owned that synth and I know it inside out. Its unique quirks and oddities makes it still really useful and fun, especially if you like more experimental electronic music.)