once again, I would love y'alls OPINIONS!

What kind of games do you think you'll feel like playing? If there's something specific it could possibly limit your options. For me personally I'd get something that could play Pokemon.

To be honest, I will recommend a PSP. The DS / 3DS are nice, but the PSP has better games in certain genres, and offers easy access to homebrew software to increase the games you have access to, even though my own was only used for a Cave Story port.

Titles I would recommend
Ape Escape P: On The Loose
Assassin's Creed: Bloodlines
BlazBlue: Continuum Shift II
Burnout Dominator
Burnout Legends
Castlevania: The Dracula X Chronicles
Coded Arms
Corpse Party
Daxter
Disgaea: Afternoon of Darkness
Disgaea 2: Dark Hero Days
Fate/Extra
Final Fantasy IV: The Complete Collection
Fortix (the king was released on PSP, the DS has no chance)
Gods Eater Burst
God of War: Chains of Olympus
God of War: Ghost of Sparta
Grand Theft Auto: Liberty City Stories
Grand Theft Auto: Vice City Stories
Guilty Gear Judgement
Harvey Birdman: Attorney at Law
Jak and Daxter: The Lost Frontier
Kenka Bancho: Badass Rumble
Kingdom Hearts: Birth by Sleep
Lunar: Silver Star Harmony
Mega Man: Powered Up
Metal Gear Solid: Peace Walker
Metal Slug Anthology
Metal Slug XX
Midnight Club: LA Remix
Monster Hunter Freedom Unite
Mortal Kombat Unchained
OMG-Z
OutRun 2006: Coast 2 Coast
Pangya Fantasy Golf
PaRappa the Rapper
Phantasy Star Portable 2
Phantom Brave: The Hermuda Triangle
Pangya Fantasy Golf
Prinny 2: Dawn of Operation Panties, Dood!
Prinny: Can I Really Be The Hero?
Ratchet & Clank: Size Matters
Resistance: Retribution
Shin Megami Tensei: Persona 3 Portable
Shinobido: Tales of the Ninja
Soul Calibur: Broken Destiny
Star Ocean: First Departure
Star Ocean: Second Evolution
Steambot Chronicles: Battle Tournament
Street Fighter Alpha 3 Max
Tales of Eternia
Tenchu: Shadow Assassins
Tony Hawk's Underground 2 Remix
Ultimate Ghosts 'n Goblins
Valkyria Chronicles II
Warriors Orochi 2
Wild ARMs XF
Ys Seven
Ys: The Oath in Felghana
ZHP: Unlosing Ranger VS Darkdeath Evilman

Even without Pokemon (beyond 3rd gen, it has a Gameboy Advance emulator), the system can offer the kinds of games you would want.

Depends on the games though I generally would say Nintendo Portables are by far the safter bet in game selections. Not that the PSP lacks games, but a good deal is basically ports/retreads of stuff found on the PS2/PS3. The PSP is easier to get "free stuff" on.

As far as as affordable, current gen it'd be the 2ds (basically the 3ds with some stuff, such as 3d removed but can play all 3ds games), but previosu gen both the DS and PSP should be pretty cheap.

GBA SP :D

Don't you have a smartphone? Why not install an emulator and buy one of those rubbery gamepad thingies that you put on your phone?

3DS XL + new Pokemon + Bravely Default + optionally Super Smash Bros
it's what I'm recommending as I own and play with it. Metal Gear Solid 3D: Snake Eater was also an interesting "little" experience on the 3DS

Valkyria Chronicles II, Final Fantasy IV: The Complete Collection, Metal Gear Solid: Peace Walker and many others would have been great to play if I had chosen the PSP but Pokemon was the deal maker for me.

An android device + PSX emulator + PSP emulator + NES emulator + SNES emulator + GB emulator + GBA emulator + DS emulator + N64 emulator on it.

I travel a lot and buy PSP, but i use it couple times ( for 4-5 years) I like games on PC but on console games are jus diffrent and i get bored even if i play tekken or NFS.

For me better idea is take laptop or good book.

i travel mostly via train or plane.

If i use car i drive or sleep :D

Buy used PSP Slim with homebrew firmware. PSP games + PS1 games in native emulator + every 8-16 bit system (plus GBA, which is actually 32 bit) games on homebrew emulators.
PSP has great screen (with better view angles than many modern mobiles) and very comfortable d-pad, so I recommend it over touchscreen android devices.