Hey dd0yl3,
Rom-wise, there are a few of them out right now, that you can download off the internet or using ROM Manager (an app in the marketplace.) A ROM is a different "version" or spin of the android operating system,which skilled developers (or devs) make. which rom you choose is really a matter of preference, and feel free to try more than one, to get a feel for what you like best. Just like the stock version of android, developers will usually try to fine-tune their ROM, and add improvements to make it a better overall experience for the user, and these are released in updates,and when an update is available, you can usually find it in the ROM manager.
A Kernel is something that tells your hardware what to do, basically, and you can also download different kernels online or in the ROM manager you can do what seems to be a common practice and do whats called "overclocking", or making your processor run faster than intended, for speed/performance boost. there are many drawbacks though. Such as the 2 most common ones- VERY fast battery drainage, and also you can damage the processor because when you force it to run faster than intended, it overheats, and overtime, may cause internal damage to it.
Its really apples to oranges. They are 2 different things, and have 2 Different purposes. so obviously there is no "Best" you just need to find a winning combo, one that suits you
