What makes a "good" lens is subjective. Case in point,
Cameraquest has a "buyer's guide" for LTM; I disagree with good chunks of it. Neither of us are wrong - it's just personal preference.
I won't spam you with photos; samples for every lens would make this post massive. But here's some "tasting notes" on some things I think are worth looking for:
In
28mm, there's four basic options for the sensible (read: not rich) user. Note that 28mm finders are typically quite expensive compared to the other sizes; I have Voigtlander's 28mm mini-finder that I bought back when prices were reasonable. Leica's 28mm viewfinders are either expensive, terrible, or a combination of both. Zeiss' 28mm viewfinder for the Contax is surprisingly decent. Canon's is probably the best buy.
Orion 28/6:
Soviet. Technically back focuses slightly as a result, but the depth of field is so huge that it doesn't make any difference. The corners are a mess at f/6, but it's largely fine at f/8. A good cheap option - if you can find a cheap one. An old friend of mine found mine in Poland. I wouldn't pay eBay prices. Expect it to need the focusing helical to be cleaned and relubricated. Takes 40.5mm filters. I'm still oddly fond of it.
Canon 28/3.5:
This is the vintage one I'd go for if I didn't own the Orion. Better in every way. Still not brilliant wide open, but a lot better at f/3.5 than the Orion is at f/6. Sometimes comes in a fancy case with an included finder. That's a hell of a deal if you can get it. Awkward filter size (Series VII, if I remember right).
Voigtlander 28/1.9 Ultron:
Great lens, but way too big on a IIIf. Feels ridiculous. I passed on it for that reason alone.
Voigtlander 28/3.5 or 28/2.8 Color Skopar:
The f/3.5 was made in the early 2000s. One of the best lenses I own. Most of them now have irrepairable haze - make sure they're completely clean. The f/2.8 one came out recently (this year?), and would be a much safer buy. Both take standard E39 filters. Worth the money. More contrasty and sharper edge-to-edge than any of the other options.
75mm only has one real option, and off the top of my head, the only reasonably-priced viewfinder is a VIOOH set to the 7.3cm setting:
75/2.5 Voigtlander Color-Heliar:
I've never used this, but here's what
@CameraQuest had to say:
"Modern multi-coated design with 6 elements in 5 groups. 10 diaphragm blades. Announced June 1999, available 9/1/99. Chrome or black, rangefinder coupled." I don't see much point to this lens - it's not enough of a step up from 50mm to justify swapping to. I'm sure it's very good, but I'd rather just keep the 50mm lens on and take two steps forwards.
For a
90mm-ish lens, some people will recommend the 85mm Canons, which are reasonably priced and probably worth a look. But personally, as far as I'm concerned, the only real choice is...
90/4 Elmar:
Lots of variation here. Early ones take A36 push-on filters and are uncoated. Later ones use E39 filters and are coated. Honestly, this is one of the best buys in all of Leica-dom. Get a clean one - haze is a real problem with these - and you won't regret it. They're cheap as chips and consistently deliver some of the best photos I've ever taken. As another bonus (if you care about such things), you can remove the lens head from an Elmar and use it on a Visoflex or Focoslide for close-up work. Can't do that with the Canons! You'll still want a hood, though - A36 ones take the collapsible
FIKUS (which can be used on a few 50mm and 135mm lenses), and the E39 ones take a clip-on and reversible
IUFOO/12575 hood. Can't really go wrong with either option.
Cheapest finder option (by a long way) will be the
VIOOH. The dedicated
SGVOO is undeniably nicer to look through, but a bit less handy. Personally, I coughed up for the
collapsible SEROO; smaller, easier to stash in a bag, and the perfect 1:1 view and easy parallax adjustment sold it for me.
I do also recommend getting a
50mm f/3.5 Elmar - the Canon you've got is decent, but having a screwmount Leica and not having a collapsible Elmar is basically criminal. The Elmar is slower, sure... but it's pretty damn sharp edge-to-edge, incredibly compact, and as long as you get a coated one that isn't full of haze, surprisingly flare-resistant.