Go to this site, and see for yourself the best one. I have this type of Action Replay (Action Replay Max) and it ROCKS. It’ll constantly uptate codes and upgrade system (I started with 1.52, now i have version 1.54)
It will let add codes you find on the internet in your (custom codes box - comes with action replay CD and user guide), and i love it.

For the Action Replay Max, the code for a Arceus Lv. 100 hold L+R and walk into the grass

94000130 fdff0000
b21c4d28 00000000
b0000004 00000000
94000130 feff0000
00000890 01ed005d
d0000000 00000000
da000000 00000892
c0000000 0000000b
0002461c 00000064
d7000000 00024620
dc000000 00000006
d2000000 00000000
02064ec8 47104a00
02064ecc 02000031
94000130 fcfe0200
02066db8 47084900
02066dbc 02000001
d2000000 00000000
94000130 fcfe0100
02066db8 95019000
02066dbc 90022000
d2000000 00000000
62000000 95019000
e2000000 0000004c
95019000 90022000
1c28b40d f0684907
1c01fd4d 2901bc0d
4902d101 49024708
00004708 02066dc1
02066d9f 00000000
95019000 69384a04
98046010 4b019a09
00004718 02064ed1
0200002c 00000000
d2000000 00000000
40510c24 20074061
04244041 940d430c
21001c28 f4c3aa0d
4801ff4f 46c04700
0206ebb1 000002e0
021c6588 00000000

Don’t worry, you can copy and paste codes in the Action Replay Code Manager (how you customize codlists, and where you upgrade AR Max and get new codes for new games) you get the CD for AR code manager in the package (box)

Either will work

the simple action replay ds already has the walk or run anywhere cheat built in, check out sites like supercheats.com or do what i have done and just type in pokemon diamond action replay codes on google and you’ll get a whole mess of cheats.

easy! Action replay Max! It’s that simple!