An ADSL2 capable modem can provide you 12mbps downstream and
3.5mbps downstream whereas an ADSL2+ capable modem can provide you 24mbps downstream and 3.5mbps upstream.
But, here in India do the ADSL operators provide such high speeds? NO. We're stuck up with 2mbps, so you can get any.
As far as I know, most of the ADSL2 modems are ADSL2+ compatible, so that doesn't make any difference.