You can dynamically load adsize based on screen resolution:
AdSize adSize = AdSize.SMART_BANNER;
DisplayMetrics dm = getResources().getDisplayMetrics();
double density = dm.density * 160;
double x = Math.pow(dm.widthPixels / density, 2);
double y = Math.pow(dm.heightPixels / density, 2);
double screenInches = Math.sqrt(x + y);
if (screenInches > 8) { // > 728 X 90
adSize = AdSize.LEADERBOARD;
} else if (screenInches > 6) { // > 468 X 60
adSize = AdSize.MEDIUM_RECTANGLE;
} else { // > 320 X 50
adSize = AdSize.BANNER;
}
// Create an ad.
adView = new AdView(this);
adView.setAdSize(adSize);
adView.setAdUnitId(AD_UNIT_ID);