i use a 400w MH and a 600w HPS throughout my entire grow and really like the results. However, if the electric bill concerns you, live in a warm climate, or if you have limited vertical grow space, definitely look into CFLs - or check out those T5 fixtures i believe they are called. Keep your plants nice and short and you can get a mix of both spectrums and use both spectrums through the whole grow - just like the Sun. Keep them nice and close and get as many as you can afford.
and start a grow journal when you do!