I have a 2000 with a PicassoII and a Phase5 2060 '060 and it runs super fast in 800x600x16 for workbench and productivity.
I have used A2000 with Blizzard2060 and PicassoIV, CV3D, EGS Spectrum and PicassoII and PicassoII feels slower in 16bit, just move the mouse between the different menus and you´ll notice how it redraws, it´s not instantaneus.
The 2000 wins for me as favorite because its built like a tank and has the most expandability.
I have a Micronik A4000 with 7 ZorroIII slots right here. On desktop models with Mediator you can fit 4 PCIs and 3 zorro cards.
Upgraded my 8-bit ISA slots to 16-bit and have every slot in my A2000 full using a bridge board.
I see little use for bridgeboard apart of using an Ethernet card. I used to have a 286 cbm bridgeboard and the sandwitch eats 2 slots.
I can easily run Windows 3.11 w/SVGA ISA & Soundblaster card, Use the Amiga and run MacOS8 all at the same time.
I can run MacOS 9 with iFusion on an A3000/A4000 :-) And I could run PC-Task with Windows3.1 too, although I see little interest in doing that.
A3000/4000 will be faster when the bus is taxed, but I have more fun on the A2000 since it has the ability to be so many more machines.
A3000/A4000 also can have faster USB2.0, can have PCI cards, have AGA, faster chipmem... and you have exactly the same posibilities of fitting a bridgeboard. Both A4000 and A3000 come with ISA slots as standard.
If "ability to be so many more machines" means fitting a PC inside the same case I can install an industrial peecee in one of the isa or pci slots way faster than old bridgeboards and interchange data using network for example.
A3000 is the best looking, but horrible cooling, few 060 options and limited Zorro/ISA slots
"few"? what do you mean by few? A3000 can use almost all A4000 060 cards, the only ones that would be problematic I remember are CyberstormMK1 (doesn´t fit on standard case) and Quickpak 060 board (only fits well on A4000T). You can fit CS MK2, CS MK3, CS PPC, GVP 060... enough for me.
ISA slots are quite useless for me :-) I prefer to use ZorroIII cards at full speed or fit PCI cards. The only use I could give to a bridgeboard would be driving an ethernet card but I can have that with Deneb for example, and enjoy relatively high in Amiga terms usb2.0 speeds with DMA.
A4000 is the fastest, but both of mine are cranky, so I am bad judge of them as I find leaking caps in all that I cross.
I have also seen dead A2000 rotten by bad batteries but that doesn´t mean A2000 are cranky. A2000 are also more unstable with those 2MB chip sandwitch like expansions.
Don´t get me wrong, I love all my miggies but A4000 is simply more powerful, just like A3000. that doesn´t mean you can´t have fun using your expanded A2000 but it will feel slower than similar A3000&A4000. And in the case of A3000 vs A4000 I prefer the later too as it has AGA and a more modern design that saves me headaches.