Ideally you should concentrate on overall strength to avoid unnecessary wear and tear and other issues. Also, it helps to visualize the body as the continuum that it is rather than parts put together as it is traditionally (and often inappropriately) viewed. This is not to say that focusing on certain areas more than others is without value. It all depends on what needs to be accomplished and the pertinent circumstances. Now, to stay in line with the topic, your lower body strength will take the priority.
Keep in mind that reactive forces (which propels us on the ground) enter our bodies through our feet as long we are engaged in any form of ambulation requiring both feet to be in contact with the ground. Walking around in gear fits the description. When you are diving your legs are you primary means of motion. Very skilled divers rely on lower body movement alone for underwater motion leaving their hands free for other tasks. I do not exactly know what you mean by "getting out the water easier" but if you referring to holding to a ladder in rough water, or climbing on a zodiac, etc, you will need upper body strength as well but keep in mind that is only a small portion of the dive in relation to the rest. Hence, the need for an overall strength program.
I do not think is fair to compare yourself to other divers when it comes to being stable on land with heavy gear on. In relation to you, you may be hoisting well over 50% of your body weight. Under certain circumstances, as when diving cold water with thick protection, extra ballast, steel tanks, or taking the tech route with doubles plus stage bottles, you may be carrying as much as your body weight (or close) on you. 60 pounds of gear is a breeze for tall diver who weighs 200 lbs while it may be overwhelming for a petite female barely breaking the scale past 110. Anyone, not just you, would be challenged under such circumstances.
The above example is another supporting point to favor lower body strength since your lower body is your base and where the reactive forces enter first. The stronger the base, the more stable the structure. It is unfortunate that flexibility, balance, endurance, etc. are still being seen as separate qualities rather than the continuum which has strength as its foundation. Yes, strength, no the biased "what do you bench?" type of strength, but rather your ability to overcome inertia.
There will be other circumstances in which your balance will be challenged. Vestibular issues, righting reflex disorders, neuromuscular issues from trauma or overuse, among many, will affect your balance, but these have to be addressed by a qualified professional and are beyond this topic.
Select a strength training program meeting your current physical levels and guides you to improvement. If possible, hire your local strength professional to help you get started. You may hear colorful terms (like core, functional, real life, etc) quite popular right now. Though they are addressing non-existing conditions and fallacies, they still can provide you with good variety for an overall conditioning so give them a go. Remember there is no such thing as one size fits all.
Take care and happy diving!
