First of all, the "Vaquero" you must be mentioning (if current or recent catalog sale) is actually the slightly smaller (aka mid) frame New Vaquero introduced 2005-ish--to replace the original (old/large-frame) Vaquero. For a reason unbeknownst to most of us, *even* Ruger is calling the newer, smaller (mid) frame model just "Vaquero" now in their literature, when it still says (because it is) "New Vaquero" on the frame. (The mid-frame .44 Special is the only NV to date that says just Vaquero on the frame).
Only in .45 is "strength" a real issue if you plan on shooting heavy and especially what's termed "Ruger only" loads intended for the NM Blackhawk's "magnum" frame. The original or old Vaquero (mentioned in the above post), discontinued for the more Colt-sized "New Vaquero" some six years ago, was basically a fixed sight, large-frame Blackhawk--same basic gun--so there is zero strength issue there.
Secondly, if shooting .357, the New Vaquero is more than adequate for most shooters' needs. It's a mostly matter of there being plenty of beef between the cylinder bores. The larger-framed Blackhawk amd old Vaquero just had more beef elsewhere too that many find unnecessary for that caliber.
Thirdly, the added cost of the New Vaqueros notwithstanding, it's a matter of your use and taste. I like the smoother lines of the Vaquero (old or New) line--and mine are mostly camp/trail/woods bumming use --where minute-of-critter accuracy is more than adequate--and not for a lot of formal target or hunting. If your intended purpose is this latter use, and/or you're shooting heavy .45s, the adjustable sighted Blackhawk is for you--or again the old Vaquero also of course. If not, you're carrying around extra weight for little to no reason--IM0. The recent years' 50th Anniversary .357 (and .44 Special) flattop Blackhawks are built on the same smaller frame as the New Vaquero, harken back to Ruger's single action origins in the 1950s, and represent a nice, handier size for those shooting the .357 and .44 Special calibers. The .44 Magnum has been only made in the larger frame original/old Vaquero and Blackhawk/Super Blackhawk, with the exception of the 50th Anniversary .44 Magnum flattop--which is a hybrid of the larger "magnum class" Blackhawk/old Vaquero cylinder frame and smaller grip-frame of the new mid-frame .357 and .44 Special flattops and New Vaquero.
One last thing, the mid-frames have an "updated" cyllinder indexing system perfectly aligning the chamber with the loading/unloading gate without stopping short or over-running, unlike the Blackhawk/old Vaquero line. While you can install a "free spin pawl" on either model which doesn't automatically stop at all (ie, place it where you want it), the mid-frame's system is an improvement for most.
While there are a lot of hammer swaps out there, most old/large-frame Vaqueros have a shorter spur, with most New Vaqueros being longer and more up (and back) swept. It's one way to spot *most* Vaqueros vs New Vaqueros at first sight. Also, other than the aforementioned .44 Specials, all of the smaller-framed Vaqueros (to date) say New Vaquero on the frame.
So, in summary, in my mind it's not a matter of "better" or "worse" but what your intended use is and aesthetic tastes run to--and your budget +/- $75-100, depending.