Sorry, I've never tried darkstar(tried to, but they won't sell out of UK to other EU states), but know many like them and they are very popular in the UK. Nicselect from e.g. everythingliquid is good nic for a good price, so sorry can't really answer which is best.
For storing nic up to 1 -2 years, I would not personally worry about plastic, but also you could
buy empty glass-bottles and rebottle yourself and store in freezer for long-term storage, many do around here.
Most VG sold in EU nowadays is from rapeseed, as they have an abundance of it locally, and EU rapeseed isn't GMO, only US rapeseed is GMO at times, but of course I cannot make a guaranty on what they use.
Personally, I and many others in EU, buy VG/PG in bulk from lubrisolve(from UK), in 5L(or bigger) containers, which I know is non-GMO EU rapeseed derived of good quality(high purity and low water). Lately the prices have gone down though from Darkstar and everythingliquid, so maybe there's not so much to save anymore as before, I dunno, but I wouldn't be surprised if both use lubrisolve VG/PG anyways. I kinda think of lubrisolve as the Essential-depot of the states, which a bunch of ECF'ers here uses

Though not as cheap though, but cheapest around in EU. Lubrisolve have COAs(test-reports) and the VG is 99.8% min and USP/PH.Eur.