To begin a new collection from scratch, I would start with a 1x18650 because of the versatility this format offers. Most of them are capable of very long runtimes at moonlight, very high outputs for short bursts, with good mode spacing between these two extremes, and they are not prohibitively large for EDC. My pick would be the S2 Baton because it can tail stand, it features my favorite UI, and it has a removable magnet, as well as a removable but sturdy clip. If the hypothetical budget permits, I would go for the Cu version because IMO, its beauty outweighs its additional weight.
When the budget allows, the next step would be a dedicated EDC in AAA format and I would go for the Titan Plus due to its solid feel, good spaced modes and beam profile. Its max output is rather functional than show-off for me, as it eliminates the need to reach out for a bigger flashlight for short duration tasks; rendering it a purposive, very handy EDC.
Armed with a Titan Plus for EDC and an S2 Baton for general purpose illumination, I admit that I would not truly need more flashlights but I would definitely badly want to have at least a soda can sized mega flooder and an ultimate thrower but I don't know if the hypothetical budget is generous enough for an X7 Marauder (not the R due to its proprietary battery) and a TN42, respectively.
I wonder if I could resist the urge of buying some keychain lights and a few headlights but you asked for a "collection", right?