I would choose a GREAT UI. Here's why.
1. The UI will ship with the console, meaning it will be stored on the NAND flash. Emulators will not ship with the console, and they will be downloaded AT THE USERS CHOOSING onto removable SD cards. The fact that the UI is stored on the NAND definitely makes it sound more permanent and thats how it should be, permanent.
2. Selling Points! In order for this thing to fly off the shelfs (errr.. internet) we need to get people interested.
Right now on openpandora.org, the first thing you see is a small but important spec sheet. This is our current Selling point, its what gets people interested. Although these selling points are more oriented to Tech Savys who know what they mean, it's great because that is our current target audience. We don't want to many average schmoes right now, we want tech savy people who can help finish the console and provide good input to make it that much better (just like where doing now). However, when the console releases this will no Longer be a good Selling point because it means nothing to a lot of people. Heres somewhat how I see it if we go with the emulator driven development.
Pandora Features (Currently working)
-Emulates All of the following consoles
Adventure Vision
Atari 2600/7800
Colecovision
Fairchild Channel F
Gameboy & Gameboy Color
Intellivision
Microvision
NES/Famicom/FDS
Odyssey/2
Sega Master System & Game Gear
Sega SG-1000
Vectrex
Amstrad
Apple II
Apple IIGS
Atari 800/XL/XE/5200
BBC Micro (possible zx-81 port, not confirmed)
Commodore 64
Commodore PET
Commodore Plus/4
Commodore VIC-20
Dragon 32/64
MSX
Oric 1
Sam Coupé
Sinclair QL
Sinclair Spectrum
Sinclair ZX-80/81
Tandy Color Computer
Tandy TRS-80
Thompson TO7-70
Atari Lynx
Genesis/Megadrive/SegaCD
NeoGeo AES/MVS
NeoGeo CD
NeoGeo Pocket/Color
Philips CDI
SNES
Turbografx-16/PC-Engine/CD-ROM
Wonderswan/Color
286 DOS PC (& 386)
Amiga
Atari ST
MacIntosh
TI 99/4A
X68000
TI-92 Calculator
Atari Jaguar
Gameboy Advance
Playstation
Virtual Boy
386 DOS PC (& 286)
N64?
-All the other crap that we know/asume
Most people are going to look at that and go "Cool! Thats a long list...but I only know 5 of them. Still impressive". Which is far enough, but lets say we go with a great UI, that would give us a selling point
Pandora Features (Currently working)
-Emulates all of the following consoles
Gameboy & Gameboy Color
Genesis/Megadrive/SegaCD
SNES
Gameboy Advance
Playstation
N64?
+More
-Commemorated and Award winning UI that has caused apple to give up on leading the market in design.
-All the other crap that we know/asume
Okay maybe that last part was a little to over the top but you get the idea
I think to this your going to get more of a "Hey Look! It emulates all the systems I wanted, and its got that really nice UI! Its got everything I could ask for!"
3. GP2x software will most likely be quickly ported to Pandora. I could easily see most of that emulator list getting done withing the first few weeks after release. That emulator list is essentially a list of many small projects. The GUI is a big project. You cannot have an entire community work on a big project. However you can have many smaller projects distributed across the entire community and expect to get them done. The emulators will come very quickly after release.
4. To have a GUI that lacks in some kind of way promotes for someone to do it better. Although their will be people making spin offs of their own GUIs and what not, if the GUI is amazing people might just not even bother trying to compete and we will have less spin offs. THIS IS GOOD
IF WE HAVE A GREAT GUI TO START WITH! Less spin offs, means less to choose from, means less confusion and incompatibility's between software.
Thank you for actually reading this entire wall of text
just my.... $3