There is a great variety to both CFLs and LED bulb replacements. I've bought CFLs both in the past, and recently which have varied greatly in how fast they'll start up, and for how long they'll continue to start up fast.
I had one in my living room which was bright, and got that bright in only a few seconds, but after a couple of years, was taking a significant amount of time to get to a reasonable brightness level, over five minutes. This is probably one of the lights in my house which gets used the most, and was rarely turned on and off in a short period of time. Admittedly an incandescent would possibly have not lasted as long, but given the price of high brightness CFLs, this one over its useful lifetime probably cost more than equivalent incandescents would have.
On the other hand, a really bright incandescent bulb often gets very hot, and can't be used in some fittings, typically enclosed ones, because of this. Even quite bright CFLs rarely get that hot.
We've bought a handful of LED lamps at work, experimenting with task lighting, because I wanted something that was very bright, but didn't generate too much heat (not good when you're inches away from the lamp). We found some cheap ones, which are basically a hundred odd small LEDs in one unit, and whilst they're OK, they aren't really bright enough for this sort of function, probably being roughly equivalent to a 30W incandescent (but only 4W or 5W iirc). I did find a ludicrously expensive unit which provides plenty of light (probably equivalent to a 150W incandescent), but it's also very large and heavy, and the cheap lamp fitting we were using couldn't really hold it up! It was over £50 iirc.
Looking around on places like eBay and Amazon, there are a lot of cheap LED lights, but they often get very indifferent reviews, and high failure rates don't seem to be uncommon with cheap units. Given the relatively high costs (even of the cheap ones), I think I'd stick with buying them from a reputable supplier, but decently bright bulbs at a moderate cost are still relatively rare, and for some of the more unusual sizes, can be damned near impossible to find.
I wonder how well the brightness will last in some of these units. Whilst there are testing bodies carrying out certification of LED bulbs, by their very nature even with accelerated testing, it takes a long time to test how well an LED will retain its brightness (months of continuous operation), so many of the reputable manufacturers haven't released fully compliant devices yet. Over driving the LEDs does produce brighter models, but at the cost of reduced lifetime, and lower efficiencies. There's a risk that less reputable suppliers will chuck out these sort of models, and give the technology a bad name.
