1 - UD 100 is a 100cc category (less power more economy) more matchable to Suzuki raider, CD 100 , Junoon e.t.c...
2 - Storm is a 125 cc category (more power some what reasonable economy given the HP) more matchable to GS 150 and CG Delux.
If I were you I would first decide the category i.e. I want a 100cc or a 125 ..then
if you are decided to 100 UD 100 will not be my choice, no doubt it looks hawt and must be of good quality but not sure, but believe me I pass by UD 100 display center every day, and the show room keepers tell themselves that this bike manufacturing halted in initial phases on few lots made a way to markets and then ended, so no new bike no new spare parts, not even old spare part, there are rumors that they are trying to get out of problems and re-launch it but not a single word from any proper official only rumors. So its a high risk if in any case you find one parked in a remote showroom.
Then comes storm, if you are very much intersted in quality with swagger then storm is you good choice, but there are some pay off to handle.
1 - Expensive spare parts (Not like CG because CG k chinese spare bhi mil jatay hain mager iskay nahi milty, sirf orignal mitlay hain or orignal hemsha mehnga hota hai).
2 - It is not italian, but from Italian brand, and its manufacturing facility is in china not in italy, just like iphone, Lenovo, Nokia all brands are europian and Americans but manufactured in china.
3 - It is imported under CUI regulation as half assembled and others bits and peicces are essembeled in pakiastan by ravi, and ravi is responsable for its spare parts as well.
4 - It can be get repaired byt any mechnic as its engine is as siple as CG engine. So not to worry.
ALARM : If you are a person who is not very fond of keeping the bike well maintained then these both bike will be a complete flop for you because both are well fabricated with lots of plastic stuff.
I hope it helps;
happy HUNTING tiger 
