If you're skeptical, try Kmeaw and then you can always switch to Rebug afterwards.
Rebug is great, but you can't go wrong with Kmeaw.
You can check the PUP to make sure you have the correct one and that it's not corrupt by running an MD5 generator on them and match what's generated to the digits below.
You can use a program like the one here : http://www.winmd5.com/
OFW 3.55 Sony md5: ca595ad9f3af8f1491d9c9b6921a8c61
CFW 3.55 kmeaw md5: 2be5e87a22bf1e7f48e98fcabd38977b
CFW 3.55.2 Rebug md5: 9f300f02a08ec16a91a17b5add399885