I would suggest a two-mode single-cell model for a good general purpose light. While I have a bunch of single-mode lights that I love, they are best for specific purposes, not general use.
I prefer the single-cell Surefires (if I can't use rechargeables) so I never need to wonder if two CR123's are going to conspire for evil and vent. If you always make sure to pair two equal-level identical model/quality/USA brand primaries, you'll most likely be fine with a 2-cell model, but I prefer rechargeables generally (which Surefires can't typically use without a drop-in lamp replacement), and single-cell for Surefires that I can't use rechargeables with.
So, what I'm leaning toward as suggestions for Surefires for general use are, depending on your preference for light levels and which mode is first up:
• E1B (80 lumens high then 5 lumens low ~ by pressure or click),
• E1L (3 lumens low then 45 lumens high ~ by pressure or click),
• L1 (10 lumens low then 65 lumens high ~ by pressure or twist)
A number of us have found that the L1 works well (and brighter) with a rechargeable, if desired. Haven't tried that in my E1B and don't have an E1L to test.
I tend to use my E1B much more than my L1 for two reasons:
• I prefer the lower low and the higher high that the E1B offers
• I prefer to click with the E1B rather than have to twist (L1) for constant-on
And I do like that the E1B can accept a wide variety of tailcap options, whereas the L1 cannot. With the Z68 tailcap, it tailstands, making the light even more versatile!
E1B w/Z68 tailcap
So I guess I've just narrowed my suggestions down to either the E1B or the E1L. If you find the lower levels more useful, the the E1L is a good way to go. If you prefer the higher levels, the E1B is great.
Lastly, as for what light I find even more useful and generally valuable than any of my Surefires? LiteFlux LF3XT. This light is simple, has a huge and infinitely variable output range, runs on CR123 or RCR123, has a very accurate (under load, even) built-in battery tester, a gorgeous smooth beam, higher high and lower low than any of the Surefires I mentioned, is simple to operate (though is programmable if you're into that sort of thing) and only costs about $65. LF3XT - a remarkable and exceptionally versatile, useful light. Here's the LF3XT on the left (next to my all time favorite budget light):