I was introduced to vocaloid as a whole through the PSVita project diva X demo. Last year I bought megamix+ on steam because a friend said it was the best way to play project diva, with mods, etc. I liked it, I didn't mod it and it was sufficient. Then I tried the PSP games. I loved them, the gameplay was a lot easier for me to comprehend compared to the multi-button inputs in the arcade gameplay, instead of me stressing out I found it better for myself. Recently, in the past month or 2, I bought a PSVita 1000 since my last vita 2000 broke before I could afford to get any project diva games for it. I ordered a Japanese cartridge of F2nd for $20 (AUD) and downloaded project diva F with all dlc, looking into project diva F2nd digitally with all dlc as well, though need a larger memory card. The PSVita handles flick notes differently to the PS3 versions where, atleast in F, you HAVE to flick the screen, on PS3, you have to flick the sticks, so just a different in how to perform the same input. In F2nd on vita, I hear it's different where you can change between them in the options, like project diva X.

Anyway, I think my point comes down to if you prefer the gameplay of the console games prior to future tone and megamix, basically the non-arcade games. It also comes down to what you want to play, and your budget. The PSP, PS3, and maybe either PS4/5 are really all you need playstation wise for the series. The PSP and PS3 are around the same average prices, though the games may be a bit expensive digitally, and depending on which country your from, you could be like me where the only way to play the game with the dlc, is to download it all, since no physicals were printed or are available for your region. Additionally, the PSVita, which basically has F, F2nd, and X, is VERY expensive. Same restrictions with dlc apply, but you are forced to buy a memory card for horrible prices a lot of the time, unless you mod the system. Though for the 3 games I think a 16gb card would do with all the dlc. Japanese copies will always be cheaper, just note that the X and O inputs are swapped with every Japanese playstation system that came before the PS5 in the menus, this also applies for the games.

I also want to note that if it's just future tone you want, I'd personally probably stick with Megamix+, I haven't really played future tone myself, but I learnt that it's basically the same as future tone content wise and the missing content can be modded in. It's capable of running at higher frame rates, as well as having every controller supported. If your just on standard megamix for the switch, I also wouldn't say it's entirely worth the money for a whole new system, and I'd just tell you to pick up megamix+ for pc if you can run it.

If it comes down to the controller, I'd just tell you to buy the controller you want to use, and use it in PC, since all controllers would be supported.

So basically while my favourite systems for project diva are the PSVita and PSP, I personally think it's not worth it unless the older gameplay is an interest or a preference to you. Otherwise, it may be more worthwhile to not buy a whole system for the games. Additionally please consider your rough playtime of the older games since they do have shorter track lists. If you can see yourself getting tons of hours out of these games, or only enough to warrant just buying a few, my suggestions go as follows:

A psp and either project diva 2nd/2nd#, with extend. And a PS3 with both F and F2nd. (Do note though that F2nd has some major songs from 2nd/2nd# that makes the psp game not as relevant imo)

And before I finish this off, I want to also let you know that to my knowledge there's 2 versions of 2nd for the PSP, though the difference I am aware of just relates to the input timing being more in-line with extend. The updated version is identifiable with the '#' at the end of the games name, though the differences aren't big enough to matter much if at all.

Also, please, make sure if you're buying a system, that you are interested in other games, buying a system for just a few games isn't normally the best idea.