Hiya and welcome here

Unfortunately, I never touched a HP calculator myself, so I don't know how much powerful they are compared to TI calcs. However:

The TI built in language from TI-73 to TI-92 and Voyage 200 graphing calcs is easier to learn than HP built in language from what I heard. However, it's very slow. I don't know if it's slower or faster than the HP language. You can still make games such as RPGs with it, though. Else there's z80 and 68k assembly, depending of the platform, and C, on 68k calcs. Most people over here do TI-BASIC (with xLIB/Celtic III), though, so we would be able to help more on that.

For calculator RPGs, if you want to see how TI-BASIC RPGs can be, check out Nyaar, Noahbaby94 game, Illusiat 13 in the projects section and other games as well. There's also a TI-83 Plus RPG nostalgia video serie on Youtube showing some TI-BASIC RPGs made from 1998 to early 2005, before xLIB and Celtic III applications came out. ASM is much harder, altough it is much more powerful. An example of what can be done in assembly would be the grayscale RPG in the calc project ideas section. There are also games such as Dying Eyes and Joltima as example.

TI-89 is more powerful when it comes to games, because the LCD is much better than the TI-83+ and because of the processor. However, they are rather expensive and harder to use in general. Fewer people uses them too it seems these days. Don't get a TI-Nspire, especially not a CAS. It barely has any programming capabilities.

I personally own almost every TI calculator models and various Casio calculators and I've been programming TI-BASIC for 8 years now and the TI-83 Plus series is still my favourite. Btw, the TI-84+ is backwards compatible with it

I don't know about u. But i CANNOT Find any help on the Ti-89. This is a problem for me.. cause im used to Ti-84, and the Ti-89 is slightly different.. and also the controls are different. So Sergepca, if you pick one of these calculators, you most likeley will stick with it (kk not to dis the Ti-89. but my freind got it and because he couldn't find any help with programming, he quit.)   )= but i don't really know if there are lots of forums out there.  So my suggestion. is Ti-84 !!! maybe SE if u want. The only benefit it gives is.. Tons more memory, and it's faster... but i doubt anyone will need that amount of memory, but the speed.. u can never have enuf!

SE = Silver Edition.

Oh come on guy, no one for defend programming on the TI89 or V200 ? ;-D
So, Z80 stay better than 68000 for real life ?

TI-89 is still used by some people. However to get help you would pretty much need to check http://www.tifreakware.net or http://tict.ticalc.org forums , since they have more 68k users. However, maybe you could still get some help over here, plus you can still announce your future projects, since a lot of us owns TI-89t

I have an 89 titanium but I gave up programing it pretty quickly as its a rather complex calc compared to the 83/84 series.

I doubt a big RPG can be done with BBC Basic, unless BBC Basic has support for both sub-routines and copying alerady existing BBC Basic programs from the archive to the RAM. If it doesn't support both these things, then forget about a large RPG, you will pretty much need to have your RPG split into 2 hour chapters, password protected (the password gets told when you finish chapter 1, for example, and when starting chapter 2, you're asked for the password the first time you run it, or the program checks the saved file (if saved files are even possible with BBC Basic) to make sure it's a valid chapter 2 save file. Then you do that with the next few chapters, with a different password each time.

Well,

After new search, I just find stuff like OTBP or TSAM on calc.
So, can we consider that a "little" 84SE as TI-Basic, BBC Basic, and ASM on calc ?

It's just amazing.

Yeah, it is quite interesting. There are nice utilities. Some we at first would never imagine possible. I am jealous of you, that can have big surprises easily. That was "cheap" fun.
Trying assembly oncalc is not great idea...

Did you mention about nspire not recommend for coding? I read this post in diagonal... Short version is nspire has no output functions (like lines, points and even text output)

I doubt a big RPG can be done with BBC Basic, unless BBC Basic has support for both sub-routines and copying alerady existing BBC Basic programs from the archive to the RAM. If it doesn't support both these things, then forget about a large RPG, you will pretty much need to have your RPG split into 2 hour chapters, password protected (the password gets told when you finish chapter 1, for example, and when starting chapter 2, you're asked for the password the first time you run it, or the program checks the saved file (if saved files are even possible with BBC Basic) to make sure it's a valid chapter 2 save file. Then you do that with the next few chapters, with a different password each time.

hmm you might be right. But I will check this once I do my last exam.