Well, the important thing is which one is better for you. I recommend you find a range that rents both and try them out there. that's the only way you'll know the answer to this question for sure.
I'm biased because I am a big Hi-Power fan and I've never fired a P99. As such, you should definitely take my comments with a big grain of salt. Since only Coronach has made a comprehensive defense of the Hi-Power, I thought I'd point out a few things in its favor.
1. P99 is 10 oz. lighter than the Hi-Power (25 oz. vs. 35 oz., meaning the HP weighs 40% more!).
It also means that the Hi-Power has more weight to tame a snappier round (.40). I'd recommend you try shooting both. My guess is that you'll find that extra weight helpful on follow-up shots and not uncomfortable to carry for long periods of time.
2. P99 is more compact, making is easier for concealed carry (7" vs 7.75" length, 1.2" vs 1.375" width).
That's
overall width. The P99 uses the barrel hood as the lockup for the slide so it has a nice blocky slide similar to the Glock. The Hi-Power's locking lugs let it use a slimmer and more traditional rounded slide with a little more thickness in the grips. On the other hand, remember the measurement above is overall width for a 9mm BHP and the .40 has a thicker slide in order to handle the heavier round.
One important measurement he left out was height. The Browning is 5" and the P99 is 5.375" This is going to be an important factor in how much the grip prints when carrying concealed. IMO, either one of these is doable; but the Browning has the edge.
4. P99 is a newer, more modern design, with excellent ergonomics (probably the best grip in the business).
The Lorcin .25 is a newer more modern design than the Hi-Power; would you rather have one based on that? Ergonomics are also very subjective - at the very least you should handle both firearms if you can't rent them and shoot them.
Capacity of magazines is really irrelevant since you specified the .40 S&W and magazine capacity for both the P99 and BHP in that caliber is 10.
Since you already own a BHP in 9mm, you have a good idea what to expect there. The extra weight in the slide of the BHP in .40 makes it a little off balance compared to the 9mm IMO. It just doesn't sit as well. The recoil also seems a little snappier although I probably couldn't tell the difference if I was blindfolded.
Lots of people whose opinion I respect like the P99 and consider it an excellent gun. I also imagine the tennifer finish is superior to the epoxy finish on the slide of the practical. Since I'm not a big fan of .40 to begin with (much prefer 9mm or.45) and I already own several Hi-Powers, I think my desire to get something new and different would probably push me towards the P99