The SD meter is the cheapest to use, and I use one myself. But I am not happy with the results it gives. My meter may be a rogue one, but I see others commenting on similar probs with theirs. Mine has always read higher than my other meters, and I get quite erratic results at times. I would not myself use the SD results to base any of my decisions on. I have just changed to the Caresense Dual from Spirit Healthcare, and I find it to be a good meter that does ketones as well (which the SD does not) the strips are a bit more expensive than the SD, but not atmospheric (approx £9.50 per 50 strips Vat Free price.)
The advice to check the Amazon reviews is sound, but remember these can be spammed and sometimes the reviews can be fake. Generally I think they now take steps to ensure that reviewers are also purchasers. Personally I go straight to the 2 star reviews since it is less likely to be faked from either point of view