If I could only have 3 "shmup consoles" they would be:
1. PCE
2. Saturn
3. PS2
PS2? Seriously? Well I guess the Cave factor is huge, but does it make up for the fact that the number of shooters on PS2 isn't very large, and most of them are on DC?
Here's the lineup of the two systems:
DC: PS2:
1. Bangai-oh 1. Baldr Force EXE
2. Baldr Force EXE 2. Do Don Pachi Dai Ou Jou
3. Chaos Field 3. Espgaluda
4. GigaWing 4. Ibara
5. GigaWing II 5. Mushihimesama
6. GunSpike/Cannon Spike 6. Psyvariar Complete
7. Gun Bird II 7. Psyvariar II Ultimate Final
8. Ikaruga 8. Homura
9. Last Hope 9. Gradius V
10. Mars Matrix 10. GigaWing Generations
11. Psyvariar 2 11. Twinkle Star Sprites: La Petite Princess (includes the AES version too)
12. Radiligy 12. Raiden III
13. Rainbow Cotton 13. Shikigami No Shiro
14. Rez 14. Shikigami No Shiro II
15. Trizeal 15. Rez
16. Twinkle Star Sprites 16. Trizeal
17. Zero Gunner II 17. Chaos Field: New Order
18. Border Down 18. Radiligy Precious
19. Shikigami No Shiro II 19. R-Type Final
20. Karasu 20. Gunbird 1 & 2
21. Trigger Heart Excelica 21. Strikers 1945 Parts I & II
22. Under Defeat 22. Sol Divide & Dragon Blaze
23. Macross M3 (only certain levels) 23. Star Soldier
24. Sengoku Aces & Sengoku Blade
So as you can see they are about equal in numbers. I'm probably missing some more PS2 games. I'm also not counting things like Metal Slug, Contra Shattered Soldier and all the retro releases like Sega Ages (I can't wait for the Galaxy Force 2 release) and Taito Memories.
And as already stated the PS2 plays PS1 games, so Raiden Project, R-Type Delta, Zanac X Zanac, Gradius Gaiden, Geppy-X, Einhander, and many more are also available.