I started out experimenting with developers; the first one I ever used was a Johnson's powder universal developer because it was cheap and could be used for both films and papers. I wouldn't recommend doing this! I eventaully standardised on Unitol because I preferred liquid concentrates and one shot use for ease and consistency. When Unitol disappeared, I switched to Rodinal, for the same basic reasons, plus the additional one of a published formula being available, so I was assured of a supply as long as I could buy the raw chemicals. Rodinal for me had another advantage of a ridiculously long shelf life. I like the acutance effect, and the grain doesn't bother me at all (I hate grain) because I don't use formats smaller than 6x6. If I were using 35mm, I might reconsider. I don't recall you saying what film sizes you use; I mainly use 5x4 where grain is not an issue at all.
I've done a little checking to refresh my memory, and SilverPrint offer R09 under the Rodinal name; Ag offer Adonal which they say is the exact Agfa formula used up until Rodinal was lost when Agfa went under. When my supply of Agfa Rodinal runs out (I have at least 5 unopened bottles) I'll go for the Adonal variant if still available. Developers work by an oxidation/reduction process; this means that they are designed to oxidise and so go off in air. Hence the advice to either use glass marbles (inert) to top up partially full bottles, of a proprietary gas spary that is heavier than air and sits on the surface. Or concertina bottles... I've had no problems with Rodinal even with none of these precautions.