Personaly i would go with a mix of both. Days of weight training, days of rest.
Or dyas of weight training, days of cardio. Cardio is great for increasing fitness if you go for explosive interval type exercise rather then endurance. It wouldnt cause weight to drop of you but you will find lifting comes on quicker.
Until you build some muscle up, i would also recommend trying to 8x 6, 4, 4, 6, 8 rep method. This starts with a lower weight at 8 reps, then a higher weight at 6, higher at 4, 4 then lower again back to 6, and again back to 8.
Really helps build up the muscles and also tendons and supporting systems needed for heavy lifting.
If you go directly into the "lift as much as you possibly can" methodology you will most likely end up with injuries and get put off, the same is true of you don allow rest days.