I personally love muscle training ! I like going to the gym for that, because if you buy weights, they'll do for a time, then you'll have to buy heavier ones. Plus, when going to the gym, you can ask staff what exercises can you do, and it's totally free (well, the gyms I tried all offered that service).
Cardio is important too if you want to have a good cardio vascular health (not sure how to formulate this in English haha). If you don't want to lose weight (well, you absolutely don't need to anyway), you have to reach a heart rate between 75% and 80% (or more) of your max rate (220 - your age = your max). Fat burning rate is around 50% (a trainer told me 35% to 55%, but on a website I found 50% to 75%), so don't stay in these ranges