if i were to get a new system i would probably get an Xbox One over a PS4, but only because most(all?) the games i would play from my 360 (NCAA Football and maybe Tales of Vespera for the xth time) are backwards compatible and i have 3 or 4 360 controllers. so i could trade in my 360 and still buy and play 360 games if i decide there are some i want since there slowly making all the top games backwards compatible.
i could also go for a PS2 that works and is old enough to be PS1 backwards compatible as there are a number of games i want to play for those. then again the games are probably expensive, so i could see what PS1/2 on PS4 games there are and consider that.
so i guess it depends on what you already have and what games you want to play, since for me i don't think there are any PS3/4 exclusives i would be interested in playing until i played a number of PS1/2 games and even SNES games. as for online, well i played a few games of Madden on Wii back in 2007 i think i was and maybe played a few matches of Brawl. other then that i don't think i have play any console games online, and i don't intend to change that so long as they charge for online. plus i spend ~$1200 for this PC in part so i could play new games on it if i want to, and the online is better on PC for the vast majority of them.