In a nut shell the PS2 was the least powerful of the three consoles last generation.
Hardly any of the games were available in progressive scan.
The Xbox1 was the most powerful, the same games released at 576i for the PS2 were available for the Xbox1 at 720p.
To get back onto the 360, the 360 really is on a par with the PS3 in terms of gaming abilities.
It completely dwarfs the abilities of the Ps2. The game graphics for one completely outclass that of the PS2, they are also all in hidef.
If you have a hidef television you will never be able to go back to the Ps2 after playing the Xbox360 for a short while.
Furthermore any good third party game for the PS2 has come out in an improved version in hidef for the Xbox 360 now.
The biggie for the Ps2, Resident Evil 5, comes out on the 360 in March.
You may need the hard drive depending on what you intend to do, but if you buy the arcade Microsoft has an offer, or at least did, where you can get 3 months of live and a 20GB hard drive all for £20.
Overall I would say to get the Xbox360 Arcade.