Welcome to the Kitz forum.
I would advise anyone not to use G.992.1 (G.DMT, ADSL1) as G.992.3 (ADSL2) uses the same number of sub-carriers as G.992.1 but uses them more efficiently.
So the choice comes down to either G.992.3 (ADSL2) or G.992.5 (ADSL2+). In theory, G.992.3 (ADSL2) has a potential maximum of 12 Mbps downstream whilst G.992.5 (ADSL2+) has a potential maximum of 24 Mbps downstream.
I would suggest that you configure your modem/router to use G.992.3 (ADSL2) modulation and check the performance over a period of a couple of weeks. After that time, reconfigure the modem/router to use G.993.5 (ADSL2+) modulation and again check the performance.
I suspect you will find that G.992.3 (ADSL2) probably gives you the best performance.