as Roter Stern says..... Vinschgau. not only does it have super weather thanks to its own mini micro climate, but it has miles after miles of trails.
i was in Vinschgau last weekend and although it wasn't super sunny it wasn't raining like the rest of the northern alps area.
in fact i rode that very trail that RS has posted. nice easy 500m climb at a ~7° gradient and there is a beer keller at the end! brill!
i used to frequent Lake Garda (Riva/Torbole area) almost every week for the last few summers. visually it is very nice, but the riding there is a little too samey, and by samey i mean rocky. the general trend is very rocky which is fine if you've got a big bike, but it does get a little tiresome after a week. there is some good stuff on the west side above and around Pregesina.
for a beginner i certainly wouldn't recommend the Lake. there doesn't seem to be much seperating the easy fire roads and the tight, rocky, lose trails. the road riding is nice, mind, but be careful where you ride as traffic on and around the lake can get silly busy.
Saalbach is also quite a trek from the Lake and although the riding is good it gets very busy with lots of park rats and stormtroopers. my GF found it a little intimidating at first but soon found it quite amusing that she was passing lads on their 180mm big bikes with her ickle Boardman FS. the trails can get clogged and after a week or so feel a little samey/motorway-like.
Vinschgau on the other hand has such a massive variety of trails that you will not get bored. mate with me last week was blown away by the amount of riding there. every thing from slow and techy to fast, flowy ear-to-ear grin inducing stuff to fast-tech-fast-tech.
the GF has been there twice and always finds something to ride (Roter Sterns vid, for example, or #5 trail, the Bierkeller Trail, Montani trail).
then of course there is Stilfser Joch for a big day out road ride:
there is also Madrijscthjoch and a few other big road climbs that go over the border into Switzerland and then come back down into Vinschgau.
the valley itself is long, about 80km from Meran to Reschen Lake/Pass. if you have two weeks there base yourself around Latsch/Naturns for a week and then head up the valley to Mals/Glurns to make the most of the riding there.
lots of the trails are marked out. although they are not specifically bike trails the locals are very accepting of bikes so long as you don't act like a dick, which is fair enough. just take heed of the "not for bike" signs. although the trails may not be very hard they are probably heavily frequented by walkers and it helps to avoid any conflict.
not sure if this link works to facebook but here are a few pics from last weekend: