As a non-radar tower controller, I would prefer you VFR. It's just one less hassle to not have to worry about the additional IFR rules and separation requirements.
That being said, there isn't that much of a difference. For the most part, VFR and IFR practice approaches are handled pretty much identically. The only exception is that I assign IFR a/c climbout instructions (heading and altitude), whereas VFR a/c only get "after completing low-approach/touch-n-go, right turnout southwest bound approved."
From a pilot and flight instructor perspective, it's ofter a tradeoff as to which is going to get you better approaches.
If you are IFR, then you will have to wait until the a/c that was cleared for the approach ahead of you either lands or begins his climbout. This often means you will have to hold or be assigned penalty vectors before you can begin your approach. However, once you are cleared for the approach, you are now almost always the #1 priority in my airspace. I will get other people out of your way as much as possible to get you what you need.
If you shoot the approach VFR, then you will likely have less time to wait flying around before you get cleared. The center which provides the approach control to my airport has no qualms about clearing multiple a/c for the ILS approach at the same time, as long as they are VFR. For that same reason, however, if you are cleared for the ILS and a King Air or Gulfstream is cleared for the same approach behind you IFR with an 50+ knot overtake, guess which one is going to get broken off the final approach course? By the same token, I'm much more likely to give VFR approaches early breakoff or altitude restrictions to seperate then from the touch-n-go pattern traffic.
So, long story short, IFR will get you better/less-interupted approaches, but if it's busy VFR will get them more frequently.
At least, that's the case with the center than runs my approach. It might be a completely different story if you're dealing with a terminal approach control who does this far more regularly and whose regs and equipment are better designed for it.