I think what folks are telling you here is forget about whether a lens is an L-series or not, at least for the time being... the red stripe alone won't necessarily make a lens "better" or not, for real world use.
First, consider what an L-series is... Canon defines it as: 1. a lens offering superior image quality and construction, 2. a lens that uses exotic glass, and 3. a lens that's fully compatible with all EOS cameras.
Not all lenses need exotic glass to do their job very well and some non-L are very well made... Example, the 100mm USM Macro, both in build an image quality that are quality "L-like", but doesn't happen to need any exotic glass so gets a gold stripe instead of a red one. Some other examples.... Look at the four Tilt-Shift lenses... They are all practically identical build, yet two are L-series and two aren't. Why? Well only the two L's need to use exotic glass. The others don't, so miss out on having the L being stamped onto them. (Granted, the two newest ones with the red stripes do have dual rotating axes, while the older non-L have only one. But that's just because the latter two haven't been updated yet. If and when they are, they may or may not become "Ls", depending mostly upon whether they get an optical make-over and need fluorite, ED, UD, or aspherical elements.)
Also, under Canon's definition, any EF-S lens that's made to fit and work on only on a crop sensor Canon can never be labelled an L, no matter how good it is. Example, the 17-55/2.8 IS, has a top image quality and even exotic glass and IS, though probably a wee bit less than L-like build and durability... Another example: the 10-22 is amazing controlling flare, best of any UWA I've seen in fact, and it uses exotic glass for top image quality. But these are both EF-S lenses so can't be fitted to full frame, 1.3X or film EOS. And thus they will never be L's.
The other big variable here is what, exactly, constitutes "best" or "better"? We all define that differently, because all of our needs and the systems we build to meet them are different.
For example, lots of folks like that 17-55/2.8 IS as a walk-around, "standard" zoom. Me, I prefer and use a longer 28-135 or 24-70. Those lenses fits into my particular system better, but doesn't necessarily make either of those a "better" lens for someone else.
Take the 24-105L as another example... In this case I'd be more likely to use one on a crop camera than on full frame... The reason is that it tends to vignette pretty heavily at the 24mm end of the zoom range. You'll see it on a full frame camera, but not so much on a cropper. On the other hand, I figure why pay 4X as much for a 24-105 than I did for a pretty much unused 28-135, that doesn't have the vignetting and otherwise pretty much matches the the L's image quality throughout the range, just is a stop slower at 135mm, uses an earlier version of I.S. and isn't quite as well built or sealed, so likely will be a little less durable.
If looking for a wide lens, no L really does the job well on crop cameras (in my humble opinion). 17-40 is the most affordable, but not particularly wide. 16-35/2.8 is a lot more expensive, and still not all that wide, though it's brighter. 14/2.8 II is very pricey, but still only gets to "pretty wide" on a cropper. Canon 10-22, Tokina 11-16 or 12-24, Sigma 8-16 or 10-20, Tamron 10-24 will all be "better" for most people looking for something wide on their crop cameras... and at whole lot lower cost!
On the other hand, it's really hard to beat the Canon 70-200mm L-series zooms. All four are excellent. Just pick the price and size you want to deal with. The f2.8 are bigger and heavier than the f4 variants. The I.S. versions offer a handy, additional feature. Of course, they vary in price and options (i.e., with the f4 lenses a tripod mount is an optional accessory... one is included with the f2.8 lenses) All of them will have a nice, red stripe on them.
It's not always a Canon lens that's the answer, either. If I were looking for something in the 100-400mm range, I'd have to seriously consider the Sigma 120-400 instead... It's optically about equal, has better stabilization, similar build and AF performance, is a dual ring type zoom (which I personally prefer) rather than push/pull, and is a whole heck of a lot cheaper. Or I'll just save up my pennies for the EF 200-400 Extender, when it comes available. Of course, I'm going to need a very, very big pile of pennies to buy the new lens! 