For fowler it dosnt matter, buy as if you are going to get corals. A little more now will save tons later.
If you are going to build a canopy use the TEK retrofits 4x54 for $220, i have seen the ICE cap retros for about $240 online (good buy, better choice). I have 2x54 on my 55 gal fowler with a few corals. I'm building my 75 gal stand now and will have 4x54 tek retros. I will possibly upgrade to Ice cap ballasts and possibly even ice cap reflectors if I go 6x54 (ice caps are slimmer, teks may not be able to get 6 in my canopy).