Window Replacement Rehab - Beginner Questions

[Eric Tom]

Hello:

I'm hoping somebody can help me answer some questions regarding window replacements as this is my first rental property. 

I have a rental property that has leaking/poor insulation windows. I am not sure when they were last replaced, but I have 4 windows each ~94in long and ~34in tall.

My tenant found mold growing near the window tracks and interior caulking as well as condensation along the edges of the window. She claimed that she heard dripping in the middle of the night and found a puddle of water on the window sill that morning, even though the windows were closed.

Questions I had were:

1. Should I get these replaced? (pictures attached) I would not want the frame to suffer water damage as a result of me not replacing...

2. If I should replace, should I get full frame replacement or insert replacements?

3. What type of windows are the best? I hear double-hung clad vinyl windows are the best bang for your buck and maintenance free windows. Would you suggest going with these?