Careful about Thinkpads - there are not like used to be. Maybe some T or X class, but there are lowend Thinkpads too. Lenovo change the image of IBM's bullet proof laptops to casual consumer grade.
But thinkpads have very good properties for cheap.
What should i avoid?
Well, I am not sure by actual offer - didn't buy Lenovo for a long time. But what can I see on wikipedia, I would avoid to ThinkPad E and Yoga stuff. As I wrote before, class T and X are premium laptop class. Class P is oriented for maximum performance and class L is midclass. Avoid any Lenovo non-ThinkPads!
Alienware PC are better like dell, Lenovo and the likes
I cheked them but they are very expensive.
Alienware
is manufactured by Dell. This class of products is designed for gaming, thus a little bit fancy and (of course) expensive.