I'm getting a new Fenwick HMG spinning rod and just wondered which would be more versatile, the 7ft. medium with a lure weight of 1/4oz. - 3/4oz. OR the 7ft. medium/heavy with a lure weight of 3/8oz. - 1oz.? I fish with a wide variety of lures, everything from senkos, rage craws and zoom lizards to crankbaits to frogs to smaller swim baits and need a rod that could adequately handle most of those.

I'm not familiar with the HMG series, but you may be able to answer your own question based solely on the lure weight recommendations.  What weights do you normally fish with your soft plastics? Add that to the weight of the bait itself and the rod where that combined weight falls somewhere in the middle of its recommendations will suit you best.  Then look at the action of the rods. A mod/fast will make casting a bit easier, but for single hook baits a faster tip will give you better hook sets.  

Both actions are "fast".

If you use bait casters get the medium, if not get the medium heavy

This is a spinning rod.

if you don't throw much stuff between 3/4-1oz i'd get the Medium.  or if you have a BC rod that can handle those higher weights, then get the Medium.

My BC rods handle 1/4 - 3/4oz. I guess like I said I'd like to have versatility so even if I don't have a lot of 1oz. lures I'm thinking maybe having the option might come in handy. I've even seen where people regularly go a little over the maximum rod lure size so maybe if the MH is rated up to 1oz. it could possibly handle 1.25 - 1.5oz. (like the Savage Gear 6" 3D line through swim baits)? I guess I'd like a rod that could handle a heavier bait but also still be able to throw senkos, craws, flukes, lizards and other similar plastic baits as well as crank baits.

I recently bought an HMG, it's a nice rod for the money.    Personally I'd go with the M unless you find yourself throwing 1 oz lures frequently. I rarely find myself tossing anything over 3/4 oz for bass. Your mileage may vary.

I went with the medium. I am going to pick up a 6'6" Berkley Lightning Rod Shock medium/heavy casting rod at my local Wal-Mart on clearance for $16 to use for heavier swim baits and lures, that is rated up to 1.25 oz. Once I learn how to use my bait cast reel that will come in handy :).