i'm new to GTD so i use a new product from Veetosoft called uTodo, a lighter version of uOrganized. However uO is pretty good for GTD, i've tried both, but is not well-known, maybe due to lack of marketing.
i prefer uTodo because is extremely fast(very keyboard firendly) and simple, i think is better than Tudumo, but uOrganized has more features and is more complex.
Here both programs are compared....