Subwoofer: Watts or Brand Name?

I've read numerous forums and reviews looking for a musical (fast, accurate) subwoofer to pair with my Harbeth P3ESRs (no movie use planned). When comparing my Harbeths to previously owned bookshelfs ($400-500) they sound tighter and less sloppy. I'm looking for the same in a subwoofer. I've owned plenty of $200-$300 subs that are a let down. I currently own an Energy S10.3 (10", 200W RMS, ported) sub. It performs very well as an invisible fill, but I want to hear "detail" in the bass. I want to hear the shape of the bass guitar string, not just that a bass guitar string was plucked. I realize that a JL Audio E110 or Rythmik F12 would do this, but I can't go more than say $500 used. Am I dreaming? I have considered a REL T5 or T5i, but I have trouble believing that replacing my 10", 200W, ported sub with a 8", 125W, sealed sub would be an improvement. Compactness isn't important. In the end I wonder if watts are the determining factor. A 10" 200W sub from a high-end brand name (REL, Rythmik, Vandersteen) versus a 10" 500W sub from a mid-level brand name (Energy, SVS, HSU, Klipsch, etc)... which do you think would perform better? The main reason I ask is that in my $500-used price range I don't know if an entry level sub from a brand name would be better than a upper range sub from a mid-level brand. Or to make life simpler, do you have any recommendations for a $500 sub (used or new) that is tight, detailed, and accurate? Maybe an 8" would accomplish this more than a 10". 

I've read over and over again that subs are expensive because they need (1) high watts and (2) thick walls/bracing. I wonder if I focus on the heaviest, highest watt subwoofer I can find from a mid-level brand...maybe it will outperform an entry level sub like the Rel T5 based purely on physics.

I’ve used this SVS SB-1000 with the Harbeth P3s with great results.
Adding to what yogiboy reports...
Am using a pair of SB1000s with Silverline Prelude Plus and Totem Forest speakers. Very pleased w/respect to the flexibility, bass-control, integration and cost of these subs. Yeah, I know, using them with "full range" floorstanders, not monitors and a pair, at that.  SVS does offer an in-house 45 day trial with free shipping even on returns if you don’t like ’em. Sorry, can’t give you a comparison against some of the higher priced options you are considering.
If I recall, there are threads about the JL subs having low quality caps.
Otherwise, I would get a pair of Vandersteen 2wq's and be done with it.
The crossovers dial in the subs perfectly and relieve the amp from reproducing the lower frequencies.
The Harbeths are great, of course, and pretty stunning with a subwoofer. (done it). I have two suggestions. The first is to get a DSpeaker Antimode 8033 room eq unit, and the second is to go for two small subs rather than one large one. With your budget, I would go for the Antimode first, and then save for two SB1000 subs.
A pair of Vandersteens for his budget of $500? Wishful thinking!
Thanks everyone. I'm still not sure if the REL T5i or SVS SB-1000 will be an improvement over my Energy S10.3. I guess I could always trial the SVS and send if back if it's not noticeably better. I've heard people note that upgrading their subwoofer made a giant difference in overall sound... even with something as affordable as the SVS. Any more advice is greatly appreciated.
The REL is a lot easier to blend if you are running your mains full range. The SVS are a great choice if you are using some type of DSP or bass management, as they are tougher to blend. Those SVS sledge amps are very powerful, but that power must be carefully managed with music. 
REL pioneered the speaker level connection for better integration, but these days many other manufacturers have followed them.
From what I could find, the Energy S10.3 is not a particularly bad subwoofer at all. In my experience the sound quality of a subwoofer depends more on room integration than on the sub itself. I started with a very good sub (a B&W PV1d) and even that did not sound great until I added an Antimode 8033 for room equalization. The result was suddenly far tighter 'faster' and more 'tunefull' bass. My next upgrade will be a second PV1d to achieve smooth bass over a much wider listening area.. See here for multiple subs:


the REL is a very musical sub at any size. Even integrate into any existing system as well.

Happy Listening!

Even easier to integrate into any existing system as well (corrected).
Get used RELs from here or Ebay…there are generally nicely maintained inexpensive RELs around that are extremely well made and sound great. Mine were bought at different times but cost around 200 bucks each...a Q150e and a Q108II.
willemj869 posts02-24-2018 2:09pmREL pioneered the speaker level connection for better integration, but these days many other manufacturers have followed them.
Lets be clear and for quite some time. Many other manufactures provide high level connectivity to accommodate systems that lack a second set of low level RCA outputs for typical subwoofer connection. Some use the high level connection in conjunction with high pass filtering to filter the main speakers low frequencies. Non that I've experienced suggest this high level connectivity as a preferred method nor have I ever experienced high level connectivity used in professional audio applications.

Information suggests REL developed their own transformer design to aid in their proprietary high level connectivity. Regardless, every REL subwoofer I've connected to my system using their high level connectivity diminished my sound stage and added a level of noise. And in all cases their integration and performance was greatly improved by Velodyne Room Optimization and, I'm told,  by other DSP methods.

The results of direct comparison are often ruthlessly revealing. In the end those results are a matter of subjective personal taste.

Robert OP,  a DSP equipped subwoofer will last you many years and more importantly will easily adapt to most any room and or speaker you choose during your audio adventures. Tighter, less sloppy, slow, musical or home theater,  are all red flag adjectives that describe subwoofers simply out of control. Add some DSP and many of those same units could sound quite good.    

The 2 RELs I've used for years work beautifully and add zero noise to my systems (they've survived changes to everything else in the rig), and with them the soundstage is utterly enhanced and a sense of realism is added to the entire thing. If this isn't the case with anybody else's system it certainly isn't due to REL's well regarded designs. I'm not a DSP fan as I don't need it in my listening room, and I think DSP gizmos take a little of the soul out of systems by notching out a naturally occurring frequency, and add extra circuitry and tone decisions decided by whomever designed the thing. For "home theater" I use an old pair of good sounding box speakers and a simple receiver (2 channel…yeah man) so clearly I'm not part of that world. Other than that, DSP is great.