If you are fishing small to medium sized streams then I think a 6wt would be perfect if you need something to throw larger than 10/12 flies. It's all realative to your casting abilities, though. If you like the mid-flex rods then you're probaby more of a relaxed/passive caster. A heavier rod would certainly help you to heave out larger flies easier but you claimed you didn't like to "fish" with your dad's 7wt as much. The best advice I can give you is to go to a fly shop and try out the 6's and 7's and see what you like the best. Personally, I think the Loomis GLX's and the Winston BIIX's are some of the best smallie rods on the market. But the Loomis rods are fast and the BIIX's are mid-fast. There are many other fine choices out there as well. If I'm wading I will either be using a fast 6 or a slow 7 on medium to large rivers. I caught this smallie with a slow 7.
LRO has a fine selection of rods that I would happily use for smallies.