I've had success up to now with a routine balanced evenly between sprints days and weights days - I like the feeling of going balls-to-the-wall on sprints and knowing that it's keeping me lean and explosive. I.e.
Day 1 - Sprints (6 x 100 and 8 x 50 / 10 x 75 and 5 x 50)
Day 2 - Weights (compound movements, medium rep ranges)
Day 3 - OFF
However I've just started a new job in central London. They give us free gym membership and a 2 hour lunch break to exercise in, amazing. The problem is though, there's literally no areas nearby where I could do sprints (no parks, hills etc, just urban civilisation). I'm trying to weigh up the balance between just twiddling my thumbs over the long lunch and sprinting at home in the evenings or mornings, or instead switching up my routine so that I could just be in the gym every day without having to worry. IF I was to go with the latter, it would make lifer easier fitting exercise in, but I'd definitely miss the sprints and I'm not sure anything in the gym would rival it. But if I did, I'd aim for something like a push/legs/pull split with added cardio:
Day 1 - Push (chest/shoulders/triceps)
Day 2 - Legs
Day 3 - Pull (back, biceps)
Day 4 - OFF
At the end of each workout, I'd glug down some BCAAs and do around 20 mins of cardio, either on the treadmill, cross-trainer or bike.