It depends whether you're talking about the original version or the updated Dream Town version. Out of the three, I'd say the Dream Town Friends takes priority, but it depends on what you like. If you're like EMF; you prefer more simple and have lots of games, you'll like Tamagotchi Friends, and if you're like the guy who thinks P's is "100 times better"; you prefer more advanced and color screened Tamagotchis which have more features and characters and etc., you'll like Tamagotchi P's.
Personally I like both of them. But here's my advice: Get them both. Everyone has different preferences, and you'll find out which one matches your preferences. I personally have good and bad things to say about both versions, but everyone else does too.
But yeah, get them both. It does not matter whether you get them both together or one before the other. If you get both of them, you'll be able to get what you're after.
Mind you though, these modern Tamagotchis are quite a lot more expensive nowadays; P's tend to go for around $25-50 on eBay; they will not be hard to find though. Tamagotchi Friends tend to go for around $10-30 and are also quite common, you shouldn't have a problem finding one. They're also on Amazon and similar sites.