The best LEGO game for you to get would be the first LEGO Batman (PSP). Its exactly like its console counterpart. The latter games you mentioned, like LOTR and Batman2, Harry Potter are all ports of the DS version, and are different than the console versions. TT took shortcuts since then.
If you dont care about them being like the console versions and yknow, fun, then get the one whose franchise you like best. --- PSN - S1lentsurviv0r