First of all, Welcome the Canreef, man! We'll be both your support group and enablers from now on, so welcome to the family.
Ok, just my opinion onj these lights but... neither. Here's why:
The metal halide, while nice and bright, is going to need some sort of actinic supplimentation unless you go to a really high colour temperature bulb, in which case growth is likely to be slow (depending on what you are wanting to keep). A 150W 20,000K bulb over 38 gallons would look great but wouldn't really cut the mustard in terms of actual output. So to get around this you will need actinic lighting and trying to set up actinic flourescents with the clip-on halide is a real pain in the arse. Trying to get two of those units over the tank would be an equal or greater pain. And on top of all that, you lose the actinic option which is actually quite nice for the evening.
Of the two options, I'd say the flourescent fixture is the better bet as you can fiddle with bulb combinations until you find something that works for you. That being said, don't be hung up on the built in timers; go to walmart and pick up a programmable plug timer for $20 (I think the manufacturer is Woods... I can get back to you on that though) and it is significantly more advanced than what you would get built in to the fixtures. Take a look around for flourescent fixtures; there's a lot of options there, though I'd recommend performance over features beacuse if you end up getting into something like SPS or clams you'll wish you have that performance.
I'm really not trying to be mean here or anything, man, so sorry if I'm sounding like a jerk.
From one guy who's start from the beginning to another, of all advice I could give to you from everything I've learned is: Do it once and do it right. What I mean by that is, get a good mental image of where you want to go and start now in planning to get there. Find local people who do this stuff and go look at their tanks and ask questions... it's worth more than gold!.
Doing upgrades along the way ends up being WAY more expensive in the long run. I know forking out the $$$ in the beginning hurts but it works out in your favour in the end. Trust me, I learned the hard way. Take a look around here, your local clubs and craigslist for used gear; you can get some high end stuff for a pretty good deal. I ended up finding
one of these for a steal (except in a 24" model). These are a much nicer set up than the clip-ons (which I also considered at one point.
I know you're just planning on two percs and some cleaner's at the moments but just you wait... Have you ever seen someone addicted to drugs? Ya, reefing ain't too far off...