Just look at Ilkka's tests and see which subs rest at the top of his list.
Size, power, shape, finish, alignment, extension, slope, configuration, crossover point are all adjustable to your particulars with DIY.
The only commercial subs that can compete somewhat, like the PB-13 Ultra, Seaton's 2X15" Submersive, and the not yet released AV123 BMF are in the $2K range, and JL Audio's 113 is in the $3K area. The larger subs from Genelec, Velo, Wilson, JL Audio, Krell, etc., are much, much, much higher priced.
The HSU, SVS, MFW, Outlaw subs of the world are no match for a good DIY sub in any category except price.
Look at the list in the attachment. Of the top 10 subwoofers (the PB-13 is counted as one subwoofer though it's on the list in four places. If iterations of the DIY subs were included, the top 10 would all be DIY), 8 are DIY. Two are commercial @ $1,700.00 and $3,000.00.
Also interesting is the fact that 7 of them are sealed subs, two are ported (one is also a sealed version of one of those which would actually make the total 7 1/2 sealed vs 1 1/2 ported vs 1 PR
) and one is PR
This is despite the fact that the vast majority of the 38 subwoofers on the list are commercial offerings.
Tom Nousaine's list has always also been topped by DIY. Yates' top awards all went to multi-K $ subs. DIY rules the roost. Always has, always will.